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LEDs - The colour of light and it's wavelength


The colour of the light we see is determined by its wavelength, which in turn is often used to denote the colour of light. The wavelengths associated with light are tiny and measured in nanometres (nm) - billionths of a metre. LEDs produce light that is almost coherent, meaning that it is almost all on one wavelength, giving very pure colours. Here is an approximate guide to the colours of light and their wavelengths.

MID INFRA-RED:

4600nm - 1600nm - Invisible.

LOWER INFRA-RED:

1300nm - 870nm - Invisible.
850nm - 810nm - Nearly invisible, a very dull red glow can sometimes be observed when viewed directly.

NEAR INFRA-RED:

780nm - Very dim cherry red when viewed directly.
770nm - Deep cherry red when viewed directly.
740nm - Deep cherry red

RED:

700nm - Deep red
660nm - Red
645nm - Bright red
630nm - "He-Ne Laser" red
620nm - Orange-red

ORANGE:

615nm - Reddish orange
610nm - Orange
605nm - Amber

YELLOW:

590nm - "Sodium" yellow
585nm - Yellow
575nm - Lemon yellow / greenish

GREEN:

570nm - lime green
555nm - Blueish lime green
550nm - Emerald green
525nm - Pure green

BLUE-GREEN:

505nm - Blueish Green
500nm - Greenish cyan
495nm - Sky blue

BLUE:

475nm - Azure blue
470nm - 460nm Bright blue
450nm - Pure blue

BLUE-VIOLET:

444nm - Deep blue
430nm - Bluish-violet

VIOLET:

405nm - Pure violet
400nm - Deep violet

NEAR ULTRA-VIOLET:

395nm - Deep purple with a slight red tinge.

ULTRA-VIOLET (UV/A):

370nm - Nearly invisible, can appear a dull, deep purple when filtered with Wood's glass.

WHITE:
White LEDs come in a wide range of shades from yellowish to purplish white. The most noticeable colour cast is generally in the centre of the beam and is usually slightly blue, surrounded by "pure" white. Colour temperatures for common types of white LED range from the low 4000°s to nearly 12000°K, with the most commonly found white LEDs being in the 6500° - 8000°K range. "Daylight" for photographic purposes is 5600°K. Most incandescent domestic light bulbs barely achieve 2500°K.