When buying light bulbs and fixtures, one specification you’ll often see is the CRI score. The CRI is the “Color Rendering Index”. What is this?
If you wanted to sum up the Color Rendering Index simply, you might say it describes the quality of the light. It is based on how accurately colors are reproduced under a light source compared to expected reference results.
The CRI is a percentage rating, so CRI 100 is the maximum score. Modern lighting technologies always fall short of this for scientific reasons.
LED and fluorescent light bulbs and fixtures have a typical CRI score of 80, which basically means the light is of sufficient quality for everyday use. A score of CRI 90 or over is considered the minimum requirement for color-critical applications, such as illuminating a print shop or photo lab.
Color rendering is one area where modern technologies cannot compete with incandescent lighting. There is a reason for this. Because incandescent lighting uses heat as its source, it emits a “continuous spectrum” of light that includes all colors of the visible spectrum. In this respect, it behaves somewhat like the sun.
Not only do incandescent bulbs emit all colors of the visible spectrum, they also do so with remarkable consistency. There is little variation between products and brands. For these reasons, the CRI score of incandescent bulbs (including halogen) is always 100 by default.
Fluorescent bulbs and LED’s usually emit a discontinuous spectrum of light and are less predictable in their output than filament bulbs. In this respect, you might say they are inferior, but in truth, perfect light is not needed for many day-to-day needs. As well, incandescent lighting always has a strong warm bias, whereas modern lighting technologies give us more choice in color temperature.
If you want to understand the difference between color temperature and color rendering, think of it this way: color temperature describes the overall color of light, whereas color rendering refers to the many underlying colors that typically make up that light.