The primary way that colors are measured for general lighting is by measuring the temperature of the light on the absolute or Kelvin scale. These typically range from a low around 2500 K, which is a very yellow light, through about 6000 K, which is a very white / blue light. Here is a listing of some approximate temperature ranges for some of the most typical general lighting colors:
- Warm White (3,000 - 3,500 K) Similar to an incandescent light, and even as low as 2700
- Natural White (4,000 - 4,500 K) Very clean white, but also not overly harsh
- Day White (5,000 - 5,600 K) Similar to natural sunlight. Much higher than this starts looking very blue.
Beyond the ability to control the light color for general comfort, as discussed in another recent post discussing some of the health benefits of LED lights, the ability to precisely control the color of an LED light can provide health benefits. In that post, we said: "By tuning the color of light emitted to match lighting needs, LEDs can reduce eye strain due to improper lighting or color shifting."
This can be valuable, because not only can the precise amount of light be provided, but the most appropriate color can be provided for the situation. For example, in a quiet church or waiting room where elevator music is playing, a softer, more yellow light can be provided. In contrast, in a work area that requires precise actions, brighter, cleaner white lights can be used to ensure small parts or precise movements can be seen more easily. Additionally, because LED lights degrade much more slowly than traditional lighting, lights maintain the selected color much longer, and also, because the light color is selected through a digital technology, the light color stays much more accurate through the lifetime of the light. Further, when lights are designed to take advantage of this flexibility, as Leading Edge Design's lights are, any fixture can be designed to emit whichever color best fits the need.
Another measurement associated with LED light color / quality is Color Rendering Index or CRI. I'll go into more detail about this in a future post. For now, know that the CRI index ranges from 0-100, with a higher number meaning that the light causes colors to be seen more closely to what is experienced in natural daylight. For the most part, any CRI greater than 70 is considered to be pretty good and anything above 80-85 is difficult to discern with the human eye.
Hopefully, this brief explanation helps you to see that LED lights today can be precisely designed to provide thousands of specific color options. To find out more, check out Leading Edge Design's FAQ's.
This measurement describes how accurately the color of an object is perceived when seen in this light and is measured by shining the light onto eight different-colored tiles, numbered R1 to R8, and analyzing the spectrum of the light reflected from the tiles. In general, CRI is quoted as the Ra value, which is the average figure across all of the test colors (R1-R8). R9, the color red, is not used in the calculation of Ra, but is important within the spectrum of human vision, so a high R9 figure can also be desirable. Typical CRI values range from 0-100, with a higher number being better (closer to rendering color similar to what is experienced in daylight). For general lighting purposes, a value of about 70 or higher is desirable, and anything above 80-85 is likely to only be detectable using computerized sensors.
So why does this matter? Most of us have experienced seeing something in a store or other venue, only to see that same object in another light and noticing that it looks like it is a different color because of the characteristics of the light in which it was seen. One example of this is on display at the San Diego Gas & Electric Energy Innovation Center in San Diego, California. Here, they have two pieces of jewelry that are both the same color, yet the one lit be a traditional incandescent light looks almost gold in color, while the one under LED lighting is very silver, which is what it looks like in daylight. See the pictures below: