Illuminant A

/ɪˈluːmɪnənt eɪ/

General Definition

Illuminant A is one of the CIE reference Standard Illuminant representing light from a common thermal tungsten source or old incandescent bulbs. This illuminant has a very low Color Temperature (around 2856 Kelvin), with its Spectral Power Distribution (SPD) concentrated at the long end of the spectrum (red and yellow range). Illuminant A is intensely warm and yellow, lacking sufficient energy in the blue and ultraviolet wavelengths. Due to its lack of resemblance to daylight and severe impact on color perception, this light should never be used to evaluate printed colors.

Real-World Usage

The main role of Illuminant A in the industry is not for print evaluation, but as a Standard Illuminant for testing color sensitivity to extremely warm lighting conditions. This light helps specialists analyze the phenomenon of Metamerism; meaning how two colors look identical under the print standard light (Illuminant D50) but are viewed differently under intensely warm and artificial light conditions (like Illuminant A). Understanding this difference is crucial for preventing complaints from customers who evaluate the final product under the warm light of their home or office.

In the printing process, using A for color evaluation is a major mistake because it renders neutral colors as yellow and warm. If a print is approved under A, it will likely have a blue or cold tint under standard light (such as D50 or even Illuminant D65). Therefore, although Illuminant A is rarely used in modern standards, recognizing its characteristics is essential for determining Color Management viewing conditions and understanding the impact of low Color Temperature on color appearance.

Consultant's Note

Consultants advise packaging manufacturers to consider Illuminant A as a "worst-case scenario" for color viewing. Warm and incandescent lights, similar to A, are still common in homes and some retail settings and can cause the customer to see the product with a color different from what you approved under D50. Therefore, materials (such as inks and substrates) should be used that have lower sensitivity to extreme light changes, minimizing the phenomenon of Metamerism.

Illuminant A is completely contrary to Illuminant D50 and Illuminant D65; it lacks the necessary spectral components to excite Optical Brightening Agents (OBA) in paper, whereas D50 and D65 contain these components. This spectral difference doubles the importance of exclusively using the Standard Illuminant D50 for print inspection to prevent inaccurate evaluations caused by warm, artificial lights like Illuminant A. Transparency with the client about the impact of ambient lights on color perception is part of professional Color Management.

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