AMPERE : The standard unit of measurement for electric current that is equal to one coulomb per second. It defines the quantity of electrons moving past a given point in a circuit during a specific period. Amp is an abbreviation.
ANSI: Abbreviation for American National Standards Institute.
ARC TUBE: A tube enclosed by the outer glass envelope of a HID lamp and made of clear quartz or ceramic that contains the arc stream.
ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers
BAFFLE: A single opaque or translucent element used to control light distribution at certain angles.
BALLAST: A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage, while limiting and regulating the lamp current during operation.
BALLAST CYCLING: Undesirable condition under which the ballast turns lamps on and off (cycles) due to the overheating of the thermal switch inside the ballast. This may be due to incorrect lamps, improper voltage being supplied, high ambient temperature around the fixture, or the early stage of ballast failure.
BALLAST EFFICIENCY FACTOR: The ballast efficiency factor (BEF) is the ballast factor (see below) divided by the input power of the ballast. The higher the BEF ( within the same lamp-ballast type ( the more efficient the ballast.
BALLAST FACTOR: The ballast factor (BF) for a specific lamp-ballast combination represents the percentage of the rated lamp lumens that will be produced by the combination.
CANDELA: Unit of luminous intensity, describing the intensity of a light source in a specific direction.
CANDELA DISTRIBUTION: A curve, often on polar coordinates, illustrating the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
CANDLEPOWER: A measure of luminous intensity of a light source in a specific direction, measured in candelas (see above).
CBM: Abbreviation for Certified Ballast Manufacturers Association.
CEC: Abbreviation for California Energy Commission.
COEFFICIENT OF UTILIZATION: The ratio of lumens from a luminaire received on the work plane to the lumens produced by the lamps alone. (Also called "CU")
COLOR RENDERING INDEX (CRI): A scale of the effect of a light source on the color appearance of an object compared to its color appearance under a reference light source. Expressed on a scale of 1 to 100, where 100 indicates no color shift. A low CRI rating suggests that the colors of objects will appear unnatural under that particular light source.
COLOR TEMPERATURE: The color temperature is a specification of the color appearance of a light source, relating the color to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the "warmth" or "coolness" of a light source. Generally, sources below 3200K are considered "warm;" while those above 4000K are considered "cool" sources.
COMPACT FLUORESCENT: A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about 10 times longer than incandescent lamps and is 3-4 times more efficacious. Also called PL, Twin-Tube, CFL, or BIAX lamps.
CONSTANT WATTAGE (CW) BALLAST: A premium type of HID ballast in which the primary and secondary coils are isolated. It is considered a high performance, high loss ballast featuring excellent output regulation.
CONSTANTWATTAGE AUTOTRANSFORMER (CWA) BALLAST: A popular type of HID ballast in which the primary and secondary coils are electrically connected. Considered an appropriate balance between cost and performance.
CONTRAST: The relationship between the luminance of an object and its background.
CRI: (SEE COLOR RENDERING INDEX)
CUT-OFF ANGLE: The angle from a fixture's vertical axis at which a reflector, louver, or other shielding device cuts off direct visibility of a lamp. It is the complementary angle of the shielding angle.
DAYLIGHT COMPENSATION: A dimming system controlled by a photocell that reduces the output of the lamps when daylight is present. As daylight levels increase, lamp intensity decreases. An energy-saving technique used in areas with significant daylight contribution.
DIFFUSE: Term describing dispersed light distribution. Refers to the scattering or softening of light.
DIFFUSER: A translucent piece of glass or plastic sheet that shields the light source in a fixture. The light transmitted throughout the diffuser will be redirected and scattered.
DIRECT GLARE: Glare produced by a direct view of light sources. Often the result of insufficiently shielded light sources. (See GLARE)
DOWNLIGHT: A type of ceiling luminaire, usually fully recessed, where most of the light is directed downward. May feature an open reflector and/or shielding device.
EFFICACY: A metric used to compare light output to energy consumption. Efficacy is measured in lumens per watt. Efficacy is similar to efficiency, but is expressed in dissimilar units. For example, if a 100-watt source produces 9000 lumens, then the efficacy is 90 lumens per watt.
ELECTROLUMINESCENT: A light source technology used in exit signs that provides uniform brightness, long lamp life (approximately eight years), while consuming very little energy (less than one watt per lamp).
ELECTRONIC BALLAST: A ballast that uses semi-conductor components to increase the frequency of fluorescent lamp operation ( typically in the 20-40 kHz range. Smaller inductive components provide the lamp current control. Fluorescent system efficiency is increased due to high frequency lamp operation.
ELECTRONIC DIMMING BALLAST: A variable output electronic fluorescent ballast.
EMI: Abbreviation for electromagnetic interference. High frequency interference (electrical noise) caused by electronic components or fluorescent lamps that interferes with the operation of electrical equipment. EMI is measured in micro-volts, and can be controlled by filters. Because EMI can interfere with communication devices, the Federal Communication Commission (FCC) has established limits for EMI.
ENERGY-SAVING BALLAST: A type of magnetic ballast designed so that the components operate more efficiently, cooler and longer than a "standard magnetic" ballast. By US law, standard magnetic ballasts can no longer be manufactured.
ENERGY-SAVING LAMP: A lower wattage lamp, generally producing fewer lumens.
FC: (SEE FOOTCANDLE)
FLUORESCENT LAMP: A light source consisting of a tube filled with argon, along with krypton or other inert gas. When electrical current is applied, the resulting arc emits ultraviolet radiation that excites the phosphors inside the lamp wall, causing them to radiate visible light.
FOOTCANDLE (FC): The English unit of measurement of the illuminance (or light level) on a surface. One footcandle is equal to one lumen per square foot.
FOOTLAMBERT: English unit of luminance. One footlambert is equal to 1/p candelas per square foot.
GLARE: The effect of brightness or differences in brightness within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.
HALOGEN: (SEE TUNGSTEN HALOGEN LAMP)
HARMONIC DISTORTION: A harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. Harmonic distortion from lighting equipment can interfere with other appliances and the operation of electric power networks. The total harmonic distortion (THD) is usually expressed as a percentage of the fundamental line current. THD for 4-foot fluorescent ballasts usually range from 20% to 40%. For compact fluorescent ballasts, THD levels greater than 50% are not uncommon.
HID: Abbreviation for high intensity discharge. Generic term describing mercury vapor, metal halide, high pressure sodium, and (informally) low pressure sodium light sources and luminaires.
HIGH-BAY: Pertains to the type of lighting in an industrial application where the ceiling is 20 feet or higher. Also describes the application itself.
HIGH OUTPUT (HO): A lamp or ballast designed to operate at higher currents (800 mA) and produce more light.
HIGH POWER FACTOR: A ballast with a 0.9 or higher rated power factor, which is achieved by using a capacitor.
HIGH PRESSURE SODIUM LAMP: A high intensity discharge (HID) lamp whose light is produced by radiation from sodium vapor (and mercury).
HOT RESTART or HOT RESTRIKE: The phenomenon of re-striking the arc in an HID light source after a momentary power loss. Hot restart occurs when the arc tube has cooled a sufficient amount.
IESNA: Abbreviation for Illuminating Engineering Society of North America.
ILLUMINANCE: A photometric term that quantifies light incident on a surface or plane. Illuminance is commonly called light level. It is expressed as lumens per square foot (footcandles), or lumens per square meter (lux).
INDIRECT GLARE: Glare produced from a reflective surface.
INSTANT START: A fluorescent circuit that ignites the lamp instantly with a very high starting voltage from the ballast. Instant start lamps have single-pin bases.
LAMP CURRENT CREST FACTOR (LCCF): The peak lamp current divided by the RMS (average) lamp current. Lamp manufacturers require <1.7 for best lamp life. An LCCF of 1.414 is a perfect sine wave.
LAMP LUMEN DEPRECIATION FACTOR (LLD): A factor that represents the reduction of lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1.
LAY-IN-TROFFER: A fluorescent fixture; usually a 2' x 4' fixture that sets or "lays" into a specific ceiling grid.
LED: Abbreviation for light emitting diode. An illumination technology used for exit signs. Consumes low wattage and has a rated life of greater than 80 years.
LENS: Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic.
LIGHT LOSS FACTOR (LLF): Factors that allow for a lighting system's operation at less than initial conditions. These factors are used to calculate maintained light levels. LLFs are divided into two categories, recoverable and non-recoverable. Examples are lamp lumen depreciation and luminaire surface depreciation.
LIFE-CYCLE COST: The total costs associated with purchasing, operating, and maintaining a system over the life of that system.
LOUVER: Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodized aluminum louvers used in parabolic fluorescent fixtures.
LOW POWER FACTOR: Essentially, an uncorrected ballast power factor of less than 0.9 (SEE NPF)
LOW-PRESSURE SODIUM: A low-pressure discharge lamp in which light is produced by radiation from sodium vapor. Considered a monochromatic light source (most colors are rendered as gray).
LOW-VOLTAGE LAMP: A lamp ( typically compact halogen ( that provides both intensity and good color rendition. Lamp operates at 12V and requires the use of a transformer. Popular lamps are MR11, MR16, and PAR36.
LOW-VOLTAGE SWITCH: A relay (magnetically-operated switch) that allows local and remote control of lights, including centralized time clock or computer control.
LUMEN: A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp.
LUMINAIRE: A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps, and connect the lamps to a power source. Also called a fixture.
LUMINAIRE EFFICIENCY: The ratio of total lumen output of a luminaire and the lumen output of the lamps, expressed as a percentage. For example, if two luminaires use the same lamps, more light will be emitted from the fixture with the higher efficiency.
LUMINANCE: A photometric term that quantifies brightness of a light source or of an illuminated surface that reflects light. It is expressed as footlamberts (English units) or candelas per square meter (Metric units).
LUX (LX): The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square meter. One lux equals 0.093 footcandles.
MAINTAINED ILLUMINANCE: Refers to light levels of a space at other than initial or rated conditions. This terms considers light loss factors such as lamp lumen depreciation, luminaire dirt depreciation, and room surface dirt depreciation.
MERCURY VAPOR LAMP: A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation from mercury vapor. Emits a blue-green cast of light. Available in clear and phosphor-coated lamps.
METAL HALIDE: A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Available in clear and phosphor-coated lamps.
MR-16: A low-voltage quartz reflector lamp, only 2" in diameter. Typically the lamp and reflector are one unit, which directs a sharp, precise beam of light.
NADIR: A reference direction directly below a luminaire, or "straight down" (0 degree angle).
NEMA: Abbreviation for National Electrical Manufacturers Association.
NIST: Abbreviation for National Institute of Standards and Technology.
NPF (NORMAL POWER FACTOR): A ballast/lamp combination in which no components (e.g., capacitors) have been added to correct the power factor, making it normal (essentially low, typically 0.5 or 50%).
OCCUPANCY SENSOR: Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared or other type.
OPTICS: A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers) or to the light emitting or light-controlling performance of a fixture.
PAR LAMP: A parabolic aluminized reflector lamp. An incandescent, metal halide, or compact fluorescent lamp used to redirect light from the source using a parabolic reflector. Lamps are available with flood or spot distributions.
PAR 36: A PAR lamp that is 36 one-eighths of an inch in diameter with a parabolic shaped reflector (SEE PAR LAMP).
PARABOLIC LUMINAIRE: A popular type of fluorescent fixture that has a louver composed of aluminum baffles curved in a parabolic shape. The resultant light distribution produced by this shape provides reduced glare, better light control, and is considered to have greater aesthetic appeal.
PARACUBE: A metallic coated plastic louver made up of small squares. Often used to replace the lens in an installed troffer to enhance its appearance. The paracube is visually comfortable, but the luminaire efficiency is lowered. Also used in rooms with computer screens because of their glare-reducing qualities.
PHOTOCELL: A light sensing device used to control luminaires and dimmers in response to detected light levels.
PHOTOMETRIC REPORT: A photometric report is a set of printed data describing the light distribution, efficiency, and zonal lumen output of a luminaire. This report is generated from laboratory testing.
POWER FACTOR: The ratio of AC volts x amps through a device to AC wattage of the device. A device such as a ballast that measures 120 volts, 1 amp, and 60 watts has a power factor of 50% (volts x amps = 120 VA, therefore 60 watts/120 VA = 0.5). Some utilities charge customers for low power factor systems.
PREHEAT: A type of ballast/lamp circuit that uses a separate starter to heat up a fluorescent lamp before high voltage is applied to start the lamp.
QUAD-TUBE LAMP: A compact fluorescent lamp with a double twin tube configuration.
RADIO FREQUENCY INTERFERENCE (RFI): Interference to the radio frequency band caused by other high frequency equipment or devices in the immediate area. Fluorescent lighting systems generate RFI.
RAPID START (RS): The most popular fluorescent lamp/ballast combination used today. This ballast quickly and efficiently preheats lamp cathodes to start the lamp. Uses a "bi-pin" base.
ROOM CAVITY RATIO (RCR): A ratio of room dimensions used to quantify how light will interact with room surfaces. A factor used in illuminance calculations.
REFLECTANCE: The ratio of light reflected from a surface to the light incident on the surface. Reflectances are often used for lighting calculations. The reflectance of a dark carpet is around 20%, and a clean white wall is roughly 50% to 60%.
REFLECTOR: The part of a light fixture that shrouds the lamps and redirects some light emitted from the lamp.
REFRACTOR: A device used to redirect the light output from a source, primarily by bending the waves of light.
RECESSED: The term used to describe the doorframe of a troffer where the lens or louver lies above the surface of the ceiling.
REGULATION: The ability of a ballast to hold constant (or nearly constant) the output watts (light output) during fluctuations in the voltage feeding of the ballast. Normally specified as +/- percent change in output compared to +/- percent change in input.
RELAY: A device that switches an electrical load on or off based on small changes in current or voltage. Examples: low voltage relay and solid state relay.
RETROFIT: Refers to upgrading a fixture, room, or building by installing new parts or equipment.
SELF-LUMINOUS EXIT SIGN: An illumination technology using phosphor-coated glass tubes filled with radioactive tritium gas. The exit sign uses no electricity and thus does not need to be hardwired.
SEMI-SPECULAR: Term describing the light reflection characteristics of a material. Some light is reflected directionally, with some amount of scatter.
SHIELDING ANGLE: The angle measured from the ceiling plane to the line of sight where the bare lamp in a luminaire becomes visible. Higher shielding angles reduce direct glare. It is the complementary angle of the cutoff angle. (See CUTOFF ANGLE).
SPACING CRITERION: A maximum distance that interior fixtures may be spaced that ensures uniform illumination on the work plane. The luminaire height above the work plane multiplied by the spacing criterion equals the center-to-center luminaire spacing.
SPECULAR: Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word describes the finish of the material used in some louvers and reflectors.
STARTER: A device used with a ballast to start preheat fluorescent lamps.
STROBOSCOPIC EFFECT: Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called "strobe effect."
T12 LAMP: Industry standard for a fluorescent lamp that is 12 one-eighths (1 inches) in diameter. Other sizes are T10 (1 inches) and T8 (1 inch) lamps.
TANDEM WIRING: A wiring option in which a ballasts is shared by two or more luminaires. This reduces labor, materials, and energy costs. Also called "master-slave" wiring.
THERMAL FACTOR: A factor used in lighting calculations that compensates for the change in light output of a fluorescent lamp due to a change in bulb wall temperature. It is applied when the lamp-ballast combination under consideration is different from that used in the photometric tests.
TRIGGER START: Type of ballast commonly used with 15-watt and 20-watt straight fluorescent lamps.
TROFFER: The term used to refer to a recessed fluorescent light fixture (combination of trough and coffer).
TUNGSTEN HALOGEN LAMP: A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens (namely iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten. Also, commonly called a quartz lamp.
TWIN-TUBE: (SEE COMPACT FLUORESCENT LAMP)
ULTRA VIOLET (UV): Invisible radiation that is shorter in wavelength and higher in frequency than visible violet light (literally beyond the violet light).
UNDERWRITERS' LABORATORIES (UL): An independent organization whose responsibilities include rigorous testing of electrical products. When products pass these tests, they can be labeled (and advertised) as "UL listed." UL tests for product safety only.
VANDAL-RESISTANT: Fixtures with rugged housings, break-resistant type shielding, and tamper-proof screws.
VCP: Abbreviation for visual comfort probability. A rating system for evaluating direct discomfort glare. This method is a subjective evaluation of visual comfort expressed as the percent of occupants of a space who will be bothered by direct glare. VCP allows for several factors: luminaire luminances at different angles of view, luminaire size, room size, luminaire mounting height, illuminance, and room surface reflectivity. VCP tables are often provided as part of photometric reports.
VERY HIGH OUTPUT (VHO): A fluorescent lamp that operates at a "very high" current (1500 mA), producing more light output than a "high output" lamp (800 mA) or standard output lamp (430 mA).
VOLT: The standard unit of measurement for electrical potential. It defines the "force" or "pressure" of electricity.
VOLTAGE: The difference in electrical potential between two points of an electrical circuit.
WALLWASHER: Describes luminaires that illuminate vertical surfaces.
WATT (W): The unit for measuring electrical power. It defines the rate of energy consumption by an electrical device when it is in operation. The energy cost of operating an electrical device is calculated as its wattage times the hours of use. In single phase circuits, it is related to volts and amps by the formula: Volts x Amps x PF = Watts. (Note: For AC circuits, PF must be included.)
WORK PLANE: The level at which work is done and at which illuminance is specified and measured. For office applications, this is typically a horizontal plane 30 inches above the floor (desk height).
ZENITH: The direction directly above the luminaire (180 angle).
Showing posts with label Lamp. Show all posts
Showing posts with label Lamp. Show all posts
Wednesday, November 16, 2011
Friday, May 20, 2011
Led-World Exclusive - All-LED-lights Mercedes-Benz CL on 2011 Shanghai Auto Show
"Innovation for Tomorrow" is the slogan of the fourteenth session of the Shanghai auto show. Based on this concept, the auto show brings many new technologies to the first facing the public. Mercedes-Benz CLS enjoys its debut on the auto show. Its 71 LED lights design makes it the focus. 2011 Shanghai Auto Show
LED has been used in automotive lighting for some time, but now there are only two kinds of vehicles applying the all-LED headlights: Mercedes-Benz CLS and Audi A8. According to manufacturers, those Audi A8 sales domestically use Xenon headlights and all LED lights are only options. Then here are the questions: What about all LED headlights? Will them become the future mainstream?
Currently, a single LED light source intensity is still less than xenon lamps. Among the majority of the car lights, LED lamp only plays a supporting role for Xenon Headlights. To reach the same brightness, even high-brightness LED requires an additional group LED lights comparing with the xenon lamps. And this group of high-brightness LED costs much and release much more heat than xenon lights.
However, the manufacturers tell us that, through some special power conversion device, LED light can issue different color temperature. The car headlights of Mercedes-Benz CLS can transform the color temperature under certain conditions and can be used as fog lights. Audi A8's daytime running lights can be converted into turn signals.
At present, LED lights have been widely used as auxiliary lights for vehicles. In turn lights, fog lights, and many other places LED Lights have replaced other sources. However, the high cost of LED brightness and thermal are the problems that R & D personnel facing. LED lighting as the main front Car Headlights is still immature. If this bottleneck breaks, LED will be the future of the automotive field.
Now, if you want to replace your car headlights, HID Xenon Car Headlight Kits are still your best option. They are providing driver better visibility and nigh vision for safety concern. NearbyExpress.com is a professional wholesaler and dropship supplier of Car Eletronics. The products are now at low China wholesale price for all its clients.
Wednesday, October 1, 2008
LED-Circuit
LED circuit
Simple LED circuit diagram
In electronics, the basic LED circuit is an electrical circuit used to power a light-emitting diode (LED). It consists of up to four components connected in series: a voltage source, a current limiting resistor, a LED, and optionally a switch to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester Two diodes may be placed in parallel in the circuit, but connected anode to cathode; the second diode may be used to protect the LED against reverse bias, which can damage the LED, or it may be another LED which is illuminated when the polarity of the voltage source is reversed.
The LEDs used will have a forward voltage specified at the intended operating current. When the voltage source Ohm's law is used to calculate the resistor that is used to attain the correct current.[4][5] The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.
This basic circuit is used in a wide range of applications, including many consumer appliances.
The formula to use to calculate the correct resistance for resistor to use is:
RESISTANCE(Ohms) =
(POWER SUPPLY VOLTAGE-LED VOLTAGE DROP)/LED CURRENT RATING
where:
Power supply voltage is the voltage of the power supply (such as a 9 volt battery)
LED voltage drop is the voltage drop across the LED (typically about 1.7 - 3.3 volts; this varies by the color of the LED)
LED current rating is the manufacturer rating of the LED (usually given in milliamperes such as 15 mA)
Simple LED circuit diagram
In electronics, the basic LED circuit is an electrical circuit used to power a light-emitting diode (LED). It consists of up to four components connected in series: a voltage source, a current limiting resistor, a LED, and optionally a switch to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester Two diodes may be placed in parallel in the circuit, but connected anode to cathode; the second diode may be used to protect the LED against reverse bias, which can damage the LED, or it may be another LED which is illuminated when the polarity of the voltage source is reversed.
The LEDs used will have a forward voltage specified at the intended operating current. When the voltage source Ohm's law is used to calculate the resistor that is used to attain the correct current.[4][5] The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.
This basic circuit is used in a wide range of applications, including many consumer appliances.
The formula to use to calculate the correct resistance for resistor to use is:
RESISTANCE(Ohms) =
(POWER SUPPLY VOLTAGE-LED VOLTAGE DROP)/LED CURRENT RATING
where:
Power supply voltage is the voltage of the power supply (such as a 9 volt battery)
LED voltage drop is the voltage drop across the LED (typically about 1.7 - 3.3 volts; this varies by the color of the LED)
LED current rating is the manufacturer rating of the LED (usually given in milliamperes such as 15 mA)
LED-Introduction
History
The phenomenon of solid state junctions producing light was discovered in the crystal detector era. In the 1960s commercial red LED's became available, and by the 1970s these were in widespread use as indicators in a very wide range of equipment. These early LED's had much too small an output to be useful as lighting. They replaced the previously widely used indicator types of filament lamps and neon. Compared to neon, indicator LED's have longer lifetimes and run on lower voltage; compared to miniature filament lamps, indicator LED's have much longer lifetimes, such that they do not require replacement, and consume less power. The lack of need for replacement also eliminates the need for bulb sockets and a user access port.
Commercial amber (yellow) and orange LED's followed, and were used where differentiation of multiple LEDs was required. For many years LED's came in infra-red, red, orange, yellow, and green. Blue, cyan, and violet LEDs finally appeared in the 1990s.
To produce a white SSL device, a blue LED was needed. In 1993, Shuji Nakamura of Nichia Corporation came up with a blue LED using gallium nitride (GaN). With this invention, it was now possible to create white light by combining the light of separate LED's (red, green, and blue), or by placing a blue LED in a package with an internal light converting phosphor. With the phosphor type, some of the blue output becomes either yellow or red and green with the result that the LED light emission appears white to the human eye.
In 2008, SSL technology advanced to the point that Sentry Equipment Corporation in Oconomowoc, Wis. was able to light its new factory almost entirely with LEDs, both interior and exterior. Although the initial cost was three times more than a traditional mixture of incandescent and fluorescent bulbs, the extra cost will be repaid within two years from electricity savings, and the bulbs should not need replacement for 20 years.
Technology overview
A single LED diode can produce only a limited amount of light, and only a single color at a time. To produce the white light necessary for SSL, light spanning the visible spectrum (red, green, and blue) must be generated in approximately correct proportions. To achieve this, three approaches are used for generating white light with LEDs: wavelength conversion, color mixing, and most recently Homoepitaxial ZnSe.
Wavelength conversion involves converting some or all of the LED’s output into visible wavelengths. Methods used to accomplish this feat include:
Blue LED & yellow phosphor – Considered the least expensive method for producing white light. Blue light from an LED is used to excite a phosphor which then re-emits yellow light. This balanced mixing of yellow and blue lights results in the appearance of white light, but produces poor color rendition (i.e., has low CRI).
Blue LED & several phosphors – Similar to the process involved with yellow phosphors, except that each excited phosphor re-emits a different color. Similarly, the resulting light is combined with the originating blue light to create white light. The resulting light, however, has a richer and broader wavelength spectrum and produces a higher color-quality light, albeit at an increased cost.
Ultraviolet (UV) LED & red, green, & blue phosphors – The UV light is used to excite the different phosphors, which are doped at measured amounts. The colors are mixed resulting in a white light with the richest and broadest wavelength spectrum.
Blue LED & quantum dots – A process by which a thin layer of nanocrystal particles containing 33 or 34 pairs of atoms, primarily cadmium and selenium, are coated on top of the LED. The blue light excites the quantum dots, resulting in a white light with a wavelength spectrum similar to UV LEDs.
Color mixing involves using multiple colors of LEDs in a lamp to produce white light. Such lamps contain a minimum of two LEDs (blue and yellow), but can also have three (red, blue, and green) or four (red, blue, green, and yellow). As no phosphors are used, there is no energy lost in the conversion process, thereby exhibiting the potential for higher efficiency.
Homoepitaxial ZnSe is a technology developed by Sumomito Electric where a LED is grown on a ZnSe substrate, which simultaneously produces blue light from the active region and yellow emission from the substrate. The resulting white light has a wavelength spectrum on par with UV LEDs. No phosphors are used, resulting in a higher efficiency white LED.
To be considered SSL, however, a multitude of LEDs must be placed close together in a lamp to add their illuminating effects. This is because an individual LED produces only a small amount of light, thereby limiting its effectiveness as a replacement light source. In the case where white LEDs are utilized in SSL, this is a relatively simple task, as all LEDs are of the same color and can be arranged in any fashion. When using the color-mixing method, however, it is more difficult to generate equivalent brightness when compared to using white LEDs in a similar lamp size. Furthermore, degradation of different LEDs at various times in a color-mixed lamp can lead to an uneven color output. Because of the inherent benefits and greater number of applications for white LED based SSL, most designs focus on utilizing them exclusively.
Driving LEDs
LEDs have very low dynamic resistance, with the same voltage drop for widely varying currents. Consequently they can not connect direct to most power sources without causing self destruction. A current control ballast is normally used, which is sometimes constant current.
Indicator LEDs
Miniature indicator LEDs are normally driven from low voltage DC via a current limiting resistor. Currents of 2mA, 10mA and 20mA are common. Some low current indicators are only rated to 2mA, and should not be driven at higher current.
Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficacy tends to reduce at low currents, but indicators running on 100uA are still practical. The cost of ultrabrights is higher than 2mA indicator LEDs.
LEDs have a low max repeat reverse voltage rating, ranging from apx 2v to 5v, and this can be a problem in some applications. Back to back LEDs are immune to this problem. These are available in single color as well as bicolor types. There are various strategies for reverse voltage handling.
In niche applications such as IR therapy, LEDs are often driven at far above rated current. This causes high failure rate and occasional LED explosions. Thus many parallel strings are used, and a safety screen and ongoing maintenance are required.
Alphanumeric LEDs
These use the same drive strategy as indicator LEDs, the only difference being the larger number of channels, each with its own resistor. 7 segment and starburst LED arrays are available in both common anode or common cathode forms.
Lighting LEDs on mains
A CR dropper (capacitor & resistor) followed by full wave rectification is the usual ballast with mains driven series-parallel LED clusters.
A single series string would minimise dropper losses, but one LED failure would extinguish the whole string. Parallelled strings increase reliability. In practice usually 3 strings or more are used.
Operation on square wave and modified sine wave (MSW) sources, such as many inverters, causes heavily increased resistor dissipation in CR droppers, and LED ballasts designed for sine wave use tend to burn on non-sine waveforms. The non-sine waveform also causes high peak LED currents, heavily shortening LED life. An inductor & rectifier makes a more suitable ballast for such use, and other options are also possible.
Lighting LEDs on low voltage
LEDs are normally operated in parallel strings of series LEDs, with the total LED voltage typically adding up to around 2/3 of the supply voltage, and resistor current control for each string.
In resistor-drive devices, LED current is then proportional to power supply (PSU) voltage minus total LED string voltage. Where battery sources are used, the PSU voltage can vary widely, causing large changes in LED current and therefore color and light output. For such applications, a constant current regulator is preferred to resistor control. Low drop-out (LDO) constant current regs also allow the total LED string voltage to be a higher percentage of PSU voltage, resulting in improved efficiency and reduced power use.
Torches run one or more lighting LEDs on a low voltage battery. These usually use a resistor ballast.
In disposable coin cell powered keyring type LED lights, the resistance of the cell itself is usually the only current limiting device. The cell should not therefore be replaced with a lower resistance type, such as one using a different battery chemistry.
Finally, an LED can be run from a single cell by use of a constant current switched mode inverter. While adding additional expense, this method provides a high level of color and brightness control, and ensures longer LED lifetime.
Comparison to other lighting technologies :
Incandescent lamps (light bulbs) create light by running electricity through a thin filament, thereby heating the filament to a very high temperature so that it glows and produces visible light. A broad range of visible frequencies are naturally produced, yielding a pleasing warm yellow or white color quality. The incandescing process, however, is highly inefficient, as over 98% of its energy input is emitted as heat.[citation needed] A standard 100 watt 120 VAC light bulb produces about 1700 lumens, about 17 lumens per watt. Incandescent lamps are relatively inexpensive to produce. The typical lifespan of a mains incandescent lamp is around 1,000 hours.[citation needed] They work well with dimmers. Most existing light fixtures are designed for the size and shape of these traditional bulbs.
Fluorescent lamps (light bulbs) work by passing electricity through mercury vapor, which in turn produces ultraviolet light. The ultraviolet light is then absorbed by a phosphor coating inside the lamp, causing it to glow, or fluoresce. While the heat generated by fluorescent lamps is much less than its incandescent counterpart, energy is still lost in generating the ultraviolet light and converting this light into visible light. If the lamp breaks exposure to mercury can occur. Linear fluorescent lamps are typically five to six times the cost of incandescent lamps[citation needed], but have life spans around 10,000 and 20,000 hours. Lifetime varies from 1,200 hours to 20,000 hours for compact fluorescent lamps.
The efficacy of fluorescent tubes with modern electronic ballast commonly averages 50 to 67 lm/W overall. Most compact fluorescents 13 watts or more with integral electronic ballasts achieve about 60 lumens/watt. They should be recycled rather than disposed to prevent mercury release. Some flicker at 100 or 120 Hz, and the quality of the light tends to be a harsh white due to the lack of a broad band of frequencies. Most are not compatible with dimmers.
Neon lamp (light bulbs) used like night-lamp in children's room. Typically a 230 V (in Europe) is rated 0.5 W of power.
SSL/LEDs LEDs come in multiple colors, which are produced without the need for filters. A white SSL can be comprised of a single high-power LED, multiple white LEDs, or from LEDs of different colors mixed to produce white light. Advantages include:
High efficiency - LEDs are now available that reliably offer over 100 lumens from a one-watt device, or much higher outputs at higher drive currents
Small size - provides design flexibility, arranged in rows, rings, clusters, or individual points
High durability - no filament or tube to break
Life span - in properly engineered lamps, LEDs can last 50,000 - 60,000 hours
Full dimmability – unlike fluorescent lamps, LEDs can be dimmed using pulse-width modulation (PWM - turning the light on and off very quickly at varying intervals). This also allows full color mixing in lamps with LEDs of different colors.[1]
Mercury-free - unlike fluorescent and most HID technologies, LEDs contain no hazardous mercury or halogen gases
However, some current models are not compatible with standard dimmers. It is not currently practical to produce high levels of room lighting. As a result, current LED screw-in light bulbs offer either low levels of light at a moderate cost, or moderate levels of light at a high cost. In contrast to other lighting technologies, LED light tends to be directional. This is a disadvantage for most general lighting applications, but can be an advantage for spot or flood lighting.
Because individual LEDs are low-voltage DC devices, implementing SSL to operate from mains AC requires well designed circuitry and a thermal case to dissipate the heat.
Applications
This garden light can use stored solar energy due to the low power consumption of its LED
Traffic lights
Automotive lighting
Stage lighting
Bicycle lighting
Flashlight (Electric torches)
Domestic lighting
Public Transit Vehicle Destination signs
Billboard displays
Floodlighting of buildings
Display lighting in art galleries to achieve a low heating effect on pictures etc.
Train lights (Now common on nearly all modern and most older MU's and Loco's in the UK)
Challenges
The current manufacturing process of white LEDs has not matured enough for them to be produced at low enough cost for widespread use. There are multiple manufacturing hurdles that must be overcome. The process used to deposit the active semiconductor layers of the LED must be improved to increase yields and manufacturing throughput. Problems with phosphors, which are needed for their ability to emit a broader wavelength spectrum of light, have also been an issue. In particular, the inability to tune the absorption and emission, and inflexibility of form have been issues in taking advantage of the phosphors spectral capabilities.
More apparent to the end user, however, is the low Color Rendering Index (CRI) of current LEDs. The current generation of LEDs, which employs mostly blue LED chip + yellow phosphor, has a CRI around 70, which is much too low for widespread use in indoor lighting. (CRI is used to measure how accurately a lighting source renders the color of objects. Sunlight and some incandescent lamps have a perfect CRI of 100, while white fluorescent lamps have CRI varying from the 50s to 95.) Better CRI LEDs are more expensive, and more research & development is needed to reduce costs. End user costs are still too high to make it a viable option, for instance, Maplin's website quotes comparable LED spots at £9.99 GBP[4] against the standard Halogen lamp twin pack which comes in at £6.49 GBP (or roughly £3.25 GBP each).
Variations of CCT (color correlated temperature) at different viewing angles present another obstacle against widespread use of white LED. It has been shown, that CCT variations can exceed 500 K, which is clearly noticeable by human observer, who is normally capable of distinguishing CCT differences of 50 to 100 K in range from 2000 K to 6000 K, which is the range of CCT variations of daylight.
LEDs also have limited temperature tolerance and falling efficiency as temperature rises. This limits the total LED power that can practically be fitted into lamps that physically replace existing filament & compact fluorescent types. R&D is needed to improve thermal characteristics.
The long life of SSL products, expected to be about 50 times the most common incandescent bulbs, poses a problem for bulb makers, whose current customers buy frequent replacements.
Research and developmet
Feb 2008 - Bilkent university - Turkey reports 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals [2].
Philips Lighting has ceased research on compact fluorescents, and is devoting the bulk of its R.& D. budget, 5 percent of the company’s global lighting revenue, to SSL
The phenomenon of solid state junctions producing light was discovered in the crystal detector era. In the 1960s commercial red LED's became available, and by the 1970s these were in widespread use as indicators in a very wide range of equipment. These early LED's had much too small an output to be useful as lighting. They replaced the previously widely used indicator types of filament lamps and neon. Compared to neon, indicator LED's have longer lifetimes and run on lower voltage; compared to miniature filament lamps, indicator LED's have much longer lifetimes, such that they do not require replacement, and consume less power. The lack of need for replacement also eliminates the need for bulb sockets and a user access port.
Commercial amber (yellow) and orange LED's followed, and were used where differentiation of multiple LEDs was required. For many years LED's came in infra-red, red, orange, yellow, and green. Blue, cyan, and violet LEDs finally appeared in the 1990s.
To produce a white SSL device, a blue LED was needed. In 1993, Shuji Nakamura of Nichia Corporation came up with a blue LED using gallium nitride (GaN). With this invention, it was now possible to create white light by combining the light of separate LED's (red, green, and blue), or by placing a blue LED in a package with an internal light converting phosphor. With the phosphor type, some of the blue output becomes either yellow or red and green with the result that the LED light emission appears white to the human eye.
In 2008, SSL technology advanced to the point that Sentry Equipment Corporation in Oconomowoc, Wis. was able to light its new factory almost entirely with LEDs, both interior and exterior. Although the initial cost was three times more than a traditional mixture of incandescent and fluorescent bulbs, the extra cost will be repaid within two years from electricity savings, and the bulbs should not need replacement for 20 years.
Technology overview
A single LED diode can produce only a limited amount of light, and only a single color at a time. To produce the white light necessary for SSL, light spanning the visible spectrum (red, green, and blue) must be generated in approximately correct proportions. To achieve this, three approaches are used for generating white light with LEDs: wavelength conversion, color mixing, and most recently Homoepitaxial ZnSe.
Wavelength conversion involves converting some or all of the LED’s output into visible wavelengths. Methods used to accomplish this feat include:
Blue LED & yellow phosphor – Considered the least expensive method for producing white light. Blue light from an LED is used to excite a phosphor which then re-emits yellow light. This balanced mixing of yellow and blue lights results in the appearance of white light, but produces poor color rendition (i.e., has low CRI).
Blue LED & several phosphors – Similar to the process involved with yellow phosphors, except that each excited phosphor re-emits a different color. Similarly, the resulting light is combined with the originating blue light to create white light. The resulting light, however, has a richer and broader wavelength spectrum and produces a higher color-quality light, albeit at an increased cost.
Ultraviolet (UV) LED & red, green, & blue phosphors – The UV light is used to excite the different phosphors, which are doped at measured amounts. The colors are mixed resulting in a white light with the richest and broadest wavelength spectrum.
Blue LED & quantum dots – A process by which a thin layer of nanocrystal particles containing 33 or 34 pairs of atoms, primarily cadmium and selenium, are coated on top of the LED. The blue light excites the quantum dots, resulting in a white light with a wavelength spectrum similar to UV LEDs.
Color mixing involves using multiple colors of LEDs in a lamp to produce white light. Such lamps contain a minimum of two LEDs (blue and yellow), but can also have three (red, blue, and green) or four (red, blue, green, and yellow). As no phosphors are used, there is no energy lost in the conversion process, thereby exhibiting the potential for higher efficiency.
Homoepitaxial ZnSe is a technology developed by Sumomito Electric where a LED is grown on a ZnSe substrate, which simultaneously produces blue light from the active region and yellow emission from the substrate. The resulting white light has a wavelength spectrum on par with UV LEDs. No phosphors are used, resulting in a higher efficiency white LED.
To be considered SSL, however, a multitude of LEDs must be placed close together in a lamp to add their illuminating effects. This is because an individual LED produces only a small amount of light, thereby limiting its effectiveness as a replacement light source. In the case where white LEDs are utilized in SSL, this is a relatively simple task, as all LEDs are of the same color and can be arranged in any fashion. When using the color-mixing method, however, it is more difficult to generate equivalent brightness when compared to using white LEDs in a similar lamp size. Furthermore, degradation of different LEDs at various times in a color-mixed lamp can lead to an uneven color output. Because of the inherent benefits and greater number of applications for white LED based SSL, most designs focus on utilizing them exclusively.
Driving LEDs
LEDs have very low dynamic resistance, with the same voltage drop for widely varying currents. Consequently they can not connect direct to most power sources without causing self destruction. A current control ballast is normally used, which is sometimes constant current.
Indicator LEDs
Miniature indicator LEDs are normally driven from low voltage DC via a current limiting resistor. Currents of 2mA, 10mA and 20mA are common. Some low current indicators are only rated to 2mA, and should not be driven at higher current.
Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficacy tends to reduce at low currents, but indicators running on 100uA are still practical. The cost of ultrabrights is higher than 2mA indicator LEDs.
LEDs have a low max repeat reverse voltage rating, ranging from apx 2v to 5v, and this can be a problem in some applications. Back to back LEDs are immune to this problem. These are available in single color as well as bicolor types. There are various strategies for reverse voltage handling.
In niche applications such as IR therapy, LEDs are often driven at far above rated current. This causes high failure rate and occasional LED explosions. Thus many parallel strings are used, and a safety screen and ongoing maintenance are required.
Alphanumeric LEDs
These use the same drive strategy as indicator LEDs, the only difference being the larger number of channels, each with its own resistor. 7 segment and starburst LED arrays are available in both common anode or common cathode forms.
Lighting LEDs on mains
A CR dropper (capacitor & resistor) followed by full wave rectification is the usual ballast with mains driven series-parallel LED clusters.
A single series string would minimise dropper losses, but one LED failure would extinguish the whole string. Parallelled strings increase reliability. In practice usually 3 strings or more are used.
Operation on square wave and modified sine wave (MSW) sources, such as many inverters, causes heavily increased resistor dissipation in CR droppers, and LED ballasts designed for sine wave use tend to burn on non-sine waveforms. The non-sine waveform also causes high peak LED currents, heavily shortening LED life. An inductor & rectifier makes a more suitable ballast for such use, and other options are also possible.
Lighting LEDs on low voltage
LEDs are normally operated in parallel strings of series LEDs, with the total LED voltage typically adding up to around 2/3 of the supply voltage, and resistor current control for each string.
In resistor-drive devices, LED current is then proportional to power supply (PSU) voltage minus total LED string voltage. Where battery sources are used, the PSU voltage can vary widely, causing large changes in LED current and therefore color and light output. For such applications, a constant current regulator is preferred to resistor control. Low drop-out (LDO) constant current regs also allow the total LED string voltage to be a higher percentage of PSU voltage, resulting in improved efficiency and reduced power use.
Torches run one or more lighting LEDs on a low voltage battery. These usually use a resistor ballast.
In disposable coin cell powered keyring type LED lights, the resistance of the cell itself is usually the only current limiting device. The cell should not therefore be replaced with a lower resistance type, such as one using a different battery chemistry.
Finally, an LED can be run from a single cell by use of a constant current switched mode inverter. While adding additional expense, this method provides a high level of color and brightness control, and ensures longer LED lifetime.
Comparison to other lighting technologies :
Incandescent lamps (light bulbs) create light by running electricity through a thin filament, thereby heating the filament to a very high temperature so that it glows and produces visible light. A broad range of visible frequencies are naturally produced, yielding a pleasing warm yellow or white color quality. The incandescing process, however, is highly inefficient, as over 98% of its energy input is emitted as heat.[citation needed] A standard 100 watt 120 VAC light bulb produces about 1700 lumens, about 17 lumens per watt. Incandescent lamps are relatively inexpensive to produce. The typical lifespan of a mains incandescent lamp is around 1,000 hours.[citation needed] They work well with dimmers. Most existing light fixtures are designed for the size and shape of these traditional bulbs.
Fluorescent lamps (light bulbs) work by passing electricity through mercury vapor, which in turn produces ultraviolet light. The ultraviolet light is then absorbed by a phosphor coating inside the lamp, causing it to glow, or fluoresce. While the heat generated by fluorescent lamps is much less than its incandescent counterpart, energy is still lost in generating the ultraviolet light and converting this light into visible light. If the lamp breaks exposure to mercury can occur. Linear fluorescent lamps are typically five to six times the cost of incandescent lamps[citation needed], but have life spans around 10,000 and 20,000 hours. Lifetime varies from 1,200 hours to 20,000 hours for compact fluorescent lamps.
The efficacy of fluorescent tubes with modern electronic ballast commonly averages 50 to 67 lm/W overall. Most compact fluorescents 13 watts or more with integral electronic ballasts achieve about 60 lumens/watt. They should be recycled rather than disposed to prevent mercury release. Some flicker at 100 or 120 Hz, and the quality of the light tends to be a harsh white due to the lack of a broad band of frequencies. Most are not compatible with dimmers.
Neon lamp (light bulbs) used like night-lamp in children's room. Typically a 230 V (in Europe) is rated 0.5 W of power.
SSL/LEDs LEDs come in multiple colors, which are produced without the need for filters. A white SSL can be comprised of a single high-power LED, multiple white LEDs, or from LEDs of different colors mixed to produce white light. Advantages include:
High efficiency - LEDs are now available that reliably offer over 100 lumens from a one-watt device, or much higher outputs at higher drive currents
Small size - provides design flexibility, arranged in rows, rings, clusters, or individual points
High durability - no filament or tube to break
Life span - in properly engineered lamps, LEDs can last 50,000 - 60,000 hours
Full dimmability – unlike fluorescent lamps, LEDs can be dimmed using pulse-width modulation (PWM - turning the light on and off very quickly at varying intervals). This also allows full color mixing in lamps with LEDs of different colors.[1]
Mercury-free - unlike fluorescent and most HID technologies, LEDs contain no hazardous mercury or halogen gases
However, some current models are not compatible with standard dimmers. It is not currently practical to produce high levels of room lighting. As a result, current LED screw-in light bulbs offer either low levels of light at a moderate cost, or moderate levels of light at a high cost. In contrast to other lighting technologies, LED light tends to be directional. This is a disadvantage for most general lighting applications, but can be an advantage for spot or flood lighting.
Because individual LEDs are low-voltage DC devices, implementing SSL to operate from mains AC requires well designed circuitry and a thermal case to dissipate the heat.
Applications
This garden light can use stored solar energy due to the low power consumption of its LED
Traffic lights
Automotive lighting
Stage lighting
Bicycle lighting
Flashlight (Electric torches)
Domestic lighting
Public Transit Vehicle Destination signs
Billboard displays
Floodlighting of buildings
Display lighting in art galleries to achieve a low heating effect on pictures etc.
Train lights (Now common on nearly all modern and most older MU's and Loco's in the UK)
Challenges
The current manufacturing process of white LEDs has not matured enough for them to be produced at low enough cost for widespread use. There are multiple manufacturing hurdles that must be overcome. The process used to deposit the active semiconductor layers of the LED must be improved to increase yields and manufacturing throughput. Problems with phosphors, which are needed for their ability to emit a broader wavelength spectrum of light, have also been an issue. In particular, the inability to tune the absorption and emission, and inflexibility of form have been issues in taking advantage of the phosphors spectral capabilities.
More apparent to the end user, however, is the low Color Rendering Index (CRI) of current LEDs. The current generation of LEDs, which employs mostly blue LED chip + yellow phosphor, has a CRI around 70, which is much too low for widespread use in indoor lighting. (CRI is used to measure how accurately a lighting source renders the color of objects. Sunlight and some incandescent lamps have a perfect CRI of 100, while white fluorescent lamps have CRI varying from the 50s to 95.) Better CRI LEDs are more expensive, and more research & development is needed to reduce costs. End user costs are still too high to make it a viable option, for instance, Maplin's website quotes comparable LED spots at £9.99 GBP[4] against the standard Halogen lamp twin pack which comes in at £6.49 GBP (or roughly £3.25 GBP each).
Variations of CCT (color correlated temperature) at different viewing angles present another obstacle against widespread use of white LED. It has been shown, that CCT variations can exceed 500 K, which is clearly noticeable by human observer, who is normally capable of distinguishing CCT differences of 50 to 100 K in range from 2000 K to 6000 K, which is the range of CCT variations of daylight.
LEDs also have limited temperature tolerance and falling efficiency as temperature rises. This limits the total LED power that can practically be fitted into lamps that physically replace existing filament & compact fluorescent types. R&D is needed to improve thermal characteristics.
The long life of SSL products, expected to be about 50 times the most common incandescent bulbs, poses a problem for bulb makers, whose current customers buy frequent replacements.
Research and developmet
Feb 2008 - Bilkent university - Turkey reports 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals [2].
Philips Lighting has ceased research on compact fluorescents, and is devoting the bulk of its R.& D. budget, 5 percent of the company’s global lighting revenue, to SSL
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