With the rapid increase in demand for LED lighting products, the market has exploded with options. How does the consumer figure out what to choose among the many different choices available?
There are a several metrics we can use to make a decision: Energy usage, light output, expected lamp life, and color temperature (CT or CCT) for example. This blog takes a look at a fifth metric – Color Rendering Index (CRI).
In walk through a garden on a clear day, the color variations of the flowers and foliage are easy to appreciate. But if you clip a rose on that walk and put it in a vase in your office, it may not look as vibrant as it did in natural light. This is because the light source determines how well we see color.
Color rendering index (CRI) is a scale from 1-100 used indicate the ability of artificial light to deliver or “render” color vitality when compared with a reference light source. This reference is an incandescent black body radiator, of which the sun is the best example. Historically, CRI was determined by comparing the time it took a group of people to match colors in a box of color chips under the reference light source vs. the amount of time needed for the same matching under the tested light source. Incandescent lamps are given a CRI of 100, as is standardized daylight. All other artificial light sources have CRIs lower than 100. It takes significantly longer to match colors under high pressure sodium lighting than under most fluorescent lighting, so it’s not surprising that HPS has a CRI of around 65 – the CRI of fluorescent lamps can range from 62 to 80. These days, CRI is determined by fun and complex algorithms, but the historic method helps us understand the principle.
When To Use Higher CRIs
Some applications demand light with higher CRIs. For example, lighting of fresh produce for sale needs the best available lighting – and vibrant color will increase sales of leafy greens and colorful fruit – consumers will have confidence in their selections and feel that they got the best value. Car dealerships need lighting with high CRI. Clothing stores, furniture stores, and textile manufacturing all need high CRI lighting. For other applications, lighting with a good CRI may be a nice bonus, but not completely necessary, as in a parking garage. For security applications, lighting that accentuates motion may be more important than lighting that makes a red car glow like fresh cherries.
For home consumers, there are two “lighting facts” programs that provide labeling found on lamps. For medium screw base type lamps, which is the most common lamp type in US household, the Federal Trade Commission has a label that provides some detail on life, appearance (CT), light output in lumens, and energy usage, but nothing at all on CRI.
Here’s an example of the FTC label:
But the Department of Energy (DOE) lighting fact program, which applies to all LED products, provides a label with much more information, and includes CRI data.
In general, the higher the CRI, the better. For home applications, if a cost difference affects your choice, concentrate on getting lamps with the best CRIs for kitchen and dining, dressing and make-up areas.