Understanding Light sources and Illuminants

Technical CIE illuminants reference list

As a general rule, all illuminants are compared against the spectral energy distribution of the so called blackbody radiator, an artificial temperature radiator that radiates light with a specific color at defined temperatures, unit [K]. While this is supposed to be a reference for incandescent lamps, it is often used as a reference for other light sources as well. Please keep in mind that for all others (e.g. the D-illuminants) these values are relative and defined with a “correlated color temperature” (CCT). Additional information about CIE illuminants can be found in CIE 15:2018.

Visualisations of the spectral curves of each of the listed Illuminants are available in the PDF.

Daylight illuminants: Illuminants that represent daylight conditions; the ones most widely in use today are:

D65: defined in 1964, D65 has become today’s standard daylight (average noon daylight from the northern sky) reference for the industry for various applications with a CCT of 6504K; described and referenced in ISO:3668, ASTM 1729 and DIN6173-2

D50: first defined in 1974, and in 1975 certified by the ISO:3664, this daylight illuminant is the reference for the printing and graphic arts industry, CCT 5003K (ISO revised in 2009); has CIE status of standard illuminant as of ISO/CIE 11664-2:2022(E)

C: old standard for average daylight from the northern sky, defined in 1931 by the CIE with a CCT of 6774K; has a significant lower UV content than the D-types; does not have CIE status of “standard illuminant” anymore

By definition, the CIE and ISO state that the “CIE standard illuminant D65 should be used in all colorimetric calculations requiring representative daylight, unless there are specific reasons for using a different illuminant.” (ISO 11664-2:2007(E)/CIE S 014-2/E:2006)

Incandescent / tungsten lamps

A: defined in 1931 as a CIE “standard illuminant”, illuminant A is intended to represent typical, domestic, tungsten-filament lighting. Its relative spectral power distribution is that of a Planckian radiator at a temperature of approximately 2856K.

Fluorescent lamps

12 fluorescent lamp types were defined by the CIE, named F1-F12, being different in the combinations of gases used and phosphors they are covered with. Among these 12, 3 are/were most commonly used in the industry and as such, are most important for colorimetric evaluations. Note that RoHS directives from the EU banned the use of mercury containing fluorescent lamps which accelerated the transition to LED solutions. As a result the use of these standards is far less common in modern standards and processes.

F2: also named “CWF” (cool white fluorescent), these lamp types have a CCT of 4230K

F7: broad-band fluorescent lamp, approximation of D65 with a CCT of 6500K

F11: also known under the name TL84, this fluorescent narrow tri-band type resembles or is mostly used as warehouse lighting and has a CCT of 4000K

Light emitting diodes (LEDs) illuminants

In its fourth edition of CIE 15 (CIE15:2018 “Colorimetry, 4th Edition”) the CIE presents recommendations for the most commonly used white LED light sources in the market at the time of its publishing. It must be noted that these LED illuminants are averages of common white types used in the market and were created after several years of studies and clustering of CIE TC 1-85.

LED-B1 - B5: Illuminants LED-B1 thru B5 are the representative illuminants for phosphor-converted blue LEDs. (CCTs: B1: 2733K / B2: 2998K / B3: 4103K / B4: 5109K / B5: 6598K)

LED-BH1: LED-BH1 is the representative illuminant for white hybrid-type LEDs. Hybrid Whites consist of a mixing of phosphor converted blue LED and red LED. (CCT: 2851K)

LED-RGB1/2: Illuminant LED-RGB1 and LED-RGB2 represent typical spectral shapes for mixing of red, green, and blue LEDs. (CCT RGB1: 2840K / RGB2: 4959K)

LED-V1/V2: LED-V1 and LED-V2 represent typical spectra shapes for phosphor-converted violet pumped LEDs. (CCT V1: 2724K / V2: 4070K)

Visualisations of the spectral curves of each of the listed Illuminants are available in the PDF.