By Patricia Fitzgerald
Ambient light is an important consideration in testing. Most manufacturers recommend performing colour-matching tests in natural light (but not looking into the sun). This is because artificial lighting will skew your colour perception—same with wearing sunglasses.
If finding natural light is inconvenient when testing indoors, buy an inexpensive illuminator like photographers use to simulate daylight and perform colour comparisons in front of it. If you are using a colourimeter, keep in mind, stray light may interfere with tests, so be sure to cap the sample chamber if so directed.
Read the full article: Busting Water Maintenance Myths