LED Lighting

Chapter 2. Key Terms

You can’t get very far talking about LED lighting without understanding the lingo. Of course, terms like “lumens” and “kilowatt-hour” are important, but a new technology always introduces new concepts to understand.

Color Rendering Index (CRI) and Color Quality Scale (CQS)

CRI is technically, according to the American National Standards Institute, the measure of how similar colors appear under illumination by a test source, compared to under a reference source that has the same correlated color temperature.

In practice, it’s often known as the color accuracy, a numerical rating of the color quality produced by a light source. Incandescent bulbs are the benchmark for the test (scoring 100) while a good LED bulb will be rated at 80 or above (this number will almost always be printed on the back of the box). Incandescents—and the sun, for that matter—are the baseline because they emit light at all points along the visible spectrum, while LEDs and CFLs have a spiked, intermittent pattern. Higher CRI value bulbs are available for graphic designers, art galleries, artists, and so forth. But they increase the cost and most consumers won’t notice a considerable difference above 80. When using a bulb with a score below 80, the results will vary based on the qualities of the particular bulb, but viewers will typically observe the color of the surrounding objects to be “dingy.” Red and blue tones will appear to be off and skin tones can look unhealthy.

CRI is determined by ...