LED illumination glossary

Luminous Quantity

Luminous Flux (lm)

The light quantity that radiates from the light source. The unit used is "lm (lumen)".

Luminous Intensity (cd = lm/sr)

The light quantity that radiates from the light source in amount of luminous flux per unit solid angle. Amount related to light source.

The unit used is cd (candela) = lm/sr (solid angle).

Illuminance (lx = lm/m2)

Indicates the brightness of the object's surface when it is lit up by the light source.

The unit used is lx (lux) = lm/m2.   The "m2" refers to the object surface area.

Luminance (nt = cd/m2)

The luminous intensity per unit area of the light source that emits light. This amount is related to the light source.

The unit is nit = cd/m2 or stilb = cd/cm2.


Color Temperature K

Indicates the spectrum energy distribution of the light irradiated by the light source using the color temperature K (Kelvin). A light source of a low value is reddish and one of a high value is bluish. A color temperature conversion filter is used to easily change the color temperature of a light source.


A filter that blocks light reflected from glass, metal, liquid surfaces, etc., that is too strong and damaging.

ND Filter

Also known as a gray filter. This is a filter that reduces the light quantity only, without impacting color reproduction.

Color Temperature Conversion Filter

A filter for changing the color temperature. The wavelength can be selected.

Diffusion Filter

A filter to diffuse light from a light source and reduce lighting irregularity.

IR (Infrared Ray) Cut-off Filter

A filter that transmits visible light while not transmitting infrared rays. There are two types of filters that do not transmit infrared rays: heat absorbing filters (or catathermic filters), which absorb infrared rays; and cold filters, which reflect infrared rays using a multilayer film.

Light Control Film

Makes diffused light more parallel using a structure in which micro-louver film is laminated with film such as PET.


Halogen Lamp

An incandescent lamp with a trace of halogen gas added to the filler gas. The halogen cycle prevents the blackening of the bulb wall. The optical output and color temperature are stable with less attenuation compared to ordinary incandescent lamps.

Metal Halide Lamp

A lamp with great light color rendering properties and high intensity that uses irradiation from various metal halogen compounds (metal halide) and mercury.


A Light Emitting Diode (LED) is a semi-conductor element that uses a fixed-direction current to a crystalline substance with a semi-conductor PN junction, generating energy in the substance and emitting the energy as light.

The basic principle was found early in the 20th century. It was confirmed through experiments that silicon carbide will radiate light if a current was applied.

Following this research, the current technology was established after we entered the 1960's. Red and green were developed first, yellow in the 1970's; and finally, blue was developed in 1993 and white in 1996.

ConstantCurrent Power Supply

A power supply that can supply a constant current even if infinite impedance or load voltage change.

ConstantVoltage Power Supply

A power supply that can supply constant voltage even if 0 impedance and load voltage change.


R. The unit is ohm (Ω). Scale that represents the difficulty of an electric current to pass. R = V/I
When there is electrical current, if the potential of a current drops by 1V (volt) per 1A (ampere), then the resistance is 1Ω.

Optical Fiber

Optical Fiber

Numerical aperture NA

This refers to the characteristic of receiving light rays transmitted through an optical fiber cross-section. This is determined by the refractive indexes of the core and cladding that make up the optical fiber.

Light Receiving Angle

Angle that allows optical fiber to receive light.