Sources used for general lighting will gradually shift in appearance to become "white" to the viewer, whether they are yellow/white like incandescent, or Lucalox® high pressure sodium lamps - or, blue/white like daylight. Within reason, the human color vision process tends to compensate or fill in for those colors lacking in the spectrum: red in the case of daylight, blue for incandescent, etc.

The eye's previous state of adaptation is also a factor. A warm environment will look even warmer to the occupants if they enter it from a cold, bluish space. It will look cooler if they have been in a yellowish or pinkish one. Then the eye slowly adapts until the space appears to be lighted with "white" light - no matter what the eye was adapted to previously.

This suggests that, while side-by-side color comparisons are an excellent way to show the differences between light sources, since the eye never becomes completely adapted to either source but to a combination of both, a final color evaluation would be best made using a relatively large space, with one color lamp lighted at a time. The ultimate test is to live with the color or colors for an extended period of time. In that way, first reactions and adaptation effects are accounted for.