Short for light-emitting diode, which is a semiconductor light source that emits light when current flows through it. Known as the 4th generation light source.


LED Phosphor is the substance that has fluorescence phenomenon, which could absorb light or other electromagnetic radiation and emitted light or radiation with longer wavelengths. It is a crucial component for white LEDs to get a broad spectrum and high color rendering index (CRI).

Surface mounted device (SMD)

SMD is a form of LED package that is encapsulated into a slim case and mounted directly onto the surface of a printed circuit board (PCB). This is an advanced technology compared to direct In-line package (DIP) LEDs and has the advantages of simple, compact and good heat dissipation.

Chip on board (COB)

COB is a manufacturing approach where the LED chips are placed directly on a printed circuit board (PCB) instead of in LED packages. By eliminating the packing, the product can be more compact and thus has higher lumen density than SMDs.

Color rendering index (CRI)

Color rendering index measures the ability of a light source compared to natural daylight to defined by CIE. CRI is measured by comparing 14 test color samples under the illumination of the reference daylight and the tested light source. Results are 14 numeric values ranged up to 100 (denoted R1 ~ R14), which indicates better color rendering ability of the light source for a value closer to 100 and could also be negative for very poor performance. CRI is the arithmetic mean of R1 ~ R14, however another parameter Ra is often preferred instead, which is the average value of R1 ~ R8.

Black-body radiator or its approximated illuminant including daylight and incandescent bulbs have a CRI of 100; fluorescent lights may be lower to 50; typical phosphor based white LEDs have of a CRI of 80. While CRI of YUJILEDS is 95 ~ 99.

Correlated color temperature (CCT)

Sometimes named as “color temperature”, although they are not exactly the same.

The color temperature is to use the temperature of an ideal black-body radiator to indicate the light color emitted from that radiator. It is measure in unit of kelvins (K), the unit of absolute temperature. Color temperature 5000K and 6500K is considered white while larger than that are called “cooler” (bluish) and lower values are called “warmer” (yellowish).

CCT is the temperature of a black-body radiator and it indicates the color of a light source which is equivalent to that black-body radiator for human eyes. CCT is more suitable for the lights that are not glowed due to thermal effect, including LEDs.

Luminous flux

Luminous Flux is the measure of the total output light of a light source that perceived by human eyes. The unit is lumen (lm). Unlike radiant flux, luminous flux is adjusted to reflect the sensitivity of human eyes to visible light by applying luminosity function.

Lumen (lm)

Lumen (lm) is the SI unit of luminous flux, indicating the total visible light emitted in unit time.


Illuminance is the measure of the luminous flux on the surface per unit area. The unit is lux (lx). So the illuminance of a light is not only related to light output, but also the distance of the measured surface and the light distribution if not isotropic.

Lux (lx)

Lux (lx) is the SI unit of illuminance, defined as lm/m2, measures the light illuminates on a surface.

Luminosity function

A luminosity function describes the sensitivity of human eyes to visible light. It is normalized to a peak value of 555nm (green light) and gradually declines to zero as the wavelength increases towards red light or decreases towards violet light.


CIE denotes the International Commission on Illumination, and is abbreviated for its French name Commission internationale de l'éclairage. It is the international authority on light, illumination, colour, and colour spaces, which was established in 1913 and is today based in Vienna, Austria.

CIE 1931 color space / CIE 1931 chromaticity diagram

CIE 1931 color space was the first quantitative color system proposed by CIE in 1931 that connected the physical light spectrum with human visions and is still widely adopted to characterize colors in industry.

CIE 1931 chromaticity diagram (or gamut chart) is a two dimensional diagram that represents the three dimensional CIE color space by dropping the representation of brightness. In the diagram, the outer curve is the spectral (or monochromatic) locus, with wavelengths shown in nanometer, which indicates the most saturated monochromatic color. The color becomes plainer in the inner region until to the white point in the center.


D50 and D65 are the standard illuminant derived by CIE, where the standard illuminant is a theoretical visible light source with well-defined SPD. D series is the successor of previous defined A, B, C illuminants, which represents natural daylight and comes in several different CCTs includes D50, D55, D65 and D75.

Luminous efficacy (LE)

Luminous Efficacy measures the efficiency of a light source. It is the ratio of the output luminousflux to the consumed electric power, measured in lumens per watts (lm/W). Depending on the target of thelight source, the efficiency could also be measured in other units (like radiant power per watts or PPFfor plants growing) if it is not for the purpose of illumination for humans.

The maximum of LE is 683 lm/W (i.e. all electric power transits into green light) according to thedefinition of luminous flux, while most current LED has a value less than 200 lm/W.

Lumen maintenance (LM)

Lumen Maintenance is used to determine the lifetime of an LED light source. Unlike traditional light sources such as incandescent lamps or fluorescent lamps, LEDs rarely fail abruptly, instead its output luminous will decline gradually over time. LM compares the luminous flux of an LED lamp after a specific time to the luminous flux when it was not used. LED is usually considered usable until LM falls to 70% (denoted as L70). Typically, the L70 lifetime of an LED is larger than 30,000 hours.

Bin or binning

The process of classifying LED components with criterions of voltages or chromaticity coordinates when manufacturing.

Alternating current (AC)

AC is the electricity form generally used for mains electricity (utility power) inside a wall socket in residential, commerical, or other buildings.The voltage and frequency are the main characteristics of AC and vary among different countries. For example, it is common to have 110V/60Hz in the US, 230V/50Hz in Germany and 220V/50Hz in China.

Direct current (DC)

DC is the electric flows in a constant direction and is commonly seen in many low power devices. For LEDs and its light fixtures, DC is only proper power source form compared to AC since the LED semiconductors only allow the electric chrages to flow in one direction.


Ultraviolet germicidal irradiation (UVGI) is an disinfection method that applies short wavelength irradiation (UV-C) by destroying the structure of microorganisms' DNAs.


Standard Deviation Color Matching (SDCM) is the deviation used in LED lighting to measure the color accuracy.The reperesentation is related to MacAdam ellipse, which is the ellipse region on a chromaticity diagram to show colors that are indistinguishable to human eyes.

Flicker free

Flicker free indicates that the flickering of the light source is unawared by either human eyes or cameras.

LED power supply

LEDs could only be driven by direct current (DC) due to the luminous principle of LEDs and thus the operation of LEDs needs extra component to convert mains electricity (AC) to DC, which is called an LED power supply. A professional LED power supply should not only be flicker-free but also have functions to protect LEDs from overcurrent and other threats.


Dimmer is used to tune the brightness of LEDs which could be connected before, after or integrated in an LED poewr supply. There are mainly two approaches to achieve this, PWM and 0-10V.

Pulse-width modulation dimmer

Pulse-width modulation (PWM) is a method of reducing the average power by chopping the constant current to discrete pulses. It has a significant advantage of saving the energy compared to 0-10V dimmers but has a risk to cause detectable flickering if the pulse frequency is not high enough. Practically, higher than 1 kHz is recommended to avoid human detected flickering, and higher than 25 kHz is recommended for 120 fps cameras.

0-10V dimmer

0-10V is an early dimming method which simply put the current to a lower level. It is dull and safe, but causes extra energy consumption by divider loads.

DMX512 decoder

DMX512 is a communication standard for stage lighting control. With a decoder, the DMX512 signal can be translated to a 3-5 channels dimming signal that controls an RGB/RGBW/RGBWW LED strip. However, one may need additional instruments to generate the DMX512 signal.



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