Which form of lighting can NOT be used for color vision testing?

The reasoning behind the assertion that Standard Illuminant A cannot be used for color vision testing is based on its spectral characteristics. Standard Illuminant A is defined by its resemblance to typical incandescent light sources, emitting a warm, yellowish light that has a spectral distribution skewed towards the longer wavelengths. This skew can adversely affect color perception, particularly in tests designed to evaluate how individuals perceive colors under more neutral lighting conditions.

In contrast, other forms of lighting mentioned, like the Macbeth Easel lamp, are typically designed to provide balanced illumination and are more suitable for assessing color vision. Standard Illuminant C, which simulates daylight, is known for providing a balanced spectrum that allows for accurate color discrimination. The 100 W tungsten bulb with Daylight C glasses modifies the light to create a more accurate representation of colors, particularly in line with natural viewing conditions.

Thus, when considering the requirements for effective and reliable color vision testing, Standard Illuminant A falls short due to its inadequate representation of a balanced white light, making it less suitable for such assessments.