# What are LEDs?

### LED Terminology

##### Emission Luminosity Iv[cd]：

Indicates the brightness when viewed from a certain direction. Expressed in units of candela (cd).
When comparing luminous intensity, it is important to consider the directional angle. Luminosity is defined as the amount of light per unit solid angle.
Light output can be focused using a package with attached lens, making it possible to provide high luminosity even with relatively small light output.
When comparing technical data, it is important to consider both the luminosity and directional angle.

##### Light Flux Φv [lm]：

Denotes the amount of light emitted from the light source, measured in units of lumens (lm).

##### Peak Wavelength λP[nm]：

The output value of the light spectrum emitted by the LED at the highest wavelength, indicated in units of nm.
The peak wavelength is considered when designing LEDs, and the dominant wavelength is actually a comparison of the wavelength when viewed with the eyes.

##### Dominant Wavelength λD[nm]：

In general, the color of an LED is determined by the wavelength. However, the wavelength corresponding to the color when viewed with the eye differs from the peak wavelength of the emission spectrum.
Units are in nm.

###### 【Example】
■Purple
：400～435nm
■Blue
：435～480nm
■Blue-Green
：480～500nm
■Green
：500～560nm
■Yellow-Green
：560～580nm
■Yellow
：580～595nm
■Orange
：595～610nm
■Red
：610～760nm

※Wavelength range, the notated color will differ slightly from the literature.

##### Chromaticity Coordinates x, y：

Stimulus values of the LED emission colors are represented by the 2-dimensional orthogonal coordinate system. The x-y coordinate system is generally used.

##### Directivity Angle 2θ1/2(deg)：

Indicates the range the light emitted from an LED radiates. Expressed in degrees.
Directivity is determined by viewing the change in light output when rotating the package, measuring from the output peak value up to what angle the light is still visible. Numerically, since directivity is normally symmetrical and covers the left and right sides when viewed from the front, it is indicated by twice the angle (±) at which the light output is half the maximum output.

##### Forward Voltage VF[V]：

Denotes the voltage generated between the anode and cathode when forward current is applied. Expressed in units of voltage (V).

##### Reverse Current Ir[A]：

Indicates the leakage current that flows between the anode and cathode in the forward direction when a reverse voltage is supplied. Expressed in units of amps (A).