Dear Reader:

The quality of electric lighting is a matter of color, and the industry has broken it into 14 shades. When a fixture is rated, each of these shades is judged through a testing method designed to assess how close the respective shade mimics the color of sunlight, on a scale of 1 to 100, with 100 being the equivalent of pure sunlight.

While this algorithm has some shortcomings (see our edition dedicated to R9 and R13), it is currently the industry standard, so we’ll explain it here.

Notice from the illustration the 14 shades of color depicted.

This scale was developed in 1965, and is still in use today. Ultimately the ratings for the various shades are amalgamated into

an average, and typically this score, known as a fixture’s Color Rendering Index, or ‘CRI’, is posted somewhere on its spec sheet.

All LED fixtures enjoy a CRI of at least 70, and by and large, the vast majority are at...