LEDs are highly monochromatic, emitting a pure color in a narrow frequency range. The color emitted from an LED is identified by peak wavelength (lpk) and measured in nanometers (nm ).

Peak wavelength is a function of the LED chip material. Although process variations are 10 NM, the 565 to 600 NM wavelength spectral region is where the sensitivity level of the human eye is highest. Therefore, it is easier to perceive color variations in yellow and amber LEDs than other colors.

LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels.

Wavelength (nm)	Color	Color Example
100-280	UV-C
280-320	UV-B
320-395	UV-A
395-430	Violet
430-450	Indigo
450-480	Blue
480-520	Blue-Green
520-555	Green
555-585	Yellow-Green
585-600	Yellow
600-615	Amber
615-625	Orange
625-640	Orange-Red
640-700	Red
700-770	Shortwave NIR
770-1100	Longwave NIR
>=1100	Infrared

Ó 2003 W. E. Johns & The LED Light Inc

The infrared band can be divided into Near Infrared (NIR) and Far Infrared (IR). Far infrared is the thermal infrared used to detect hot objects or see heat leaks in buildings, and is way beyond the range of LEDs. (NIR can be further divided into two bands, longwave and shortwave NIR, based on how film and CCD cameras react, which I'll get into elsewhere, elsewhen, and elsewhy.)

Infrared LEDs are sometimes called IREDs (Infra Red Emitting Diodes).

Ultraviolet light is divided into three bands: UV-A, which is fairly innocuous; UV-B, which causes sunburns; and UV-C, which kills things. Most UV-B and all UV-C from the sun is filtered out by the ozone layer, so we get very little of it naturally. LEDs emit UV-A.

400 nm is a pretty common wavelength for UV LEDs. This is right on the border between the violet and ultraviolet, so a significant portion of the light emitted is visible. For this reason 400 nm UV LEDs are sometimes rated in millicandela, even though as much as half of their energy is invisible. LEDs with lower wavelengths, such as 380nm, are usually not rated in millicandela, but in milliwatts.

LEDs are very bright. DO NOT look directly into the LED light!! The light can be intense enough to injure human eyes.