Most of us have heard the story of a football team painting the visitors’ locker room pink to psych out the opposing players before they take the field. Studies have shown that color can indeed have an effect, significant at times, on the way a person feels in a space and their overall mood. More specifically, red can invoke feelings of high energy and passion, yellow can increase levels of optimism, blue tends to calm, and orange can bring out one’s nurturing side.
Since color is just a certain wavelength of light that is reflected from a surface back to the eye, the nature of that source can have a significant impact on how we experience color. The measure of how accurately a light source shows color is called its Color Rendering Index, or CRI. The higher the CRI number, the truer a light source renders color. Daytime sunlight contains the most energy across the full visible spectrum of light and is the best light source to render color, thus the sun has a CRI of 100. You can imagine though, that the warm hues of dusk or dawn render color differently than a bright cloudless early afternoon. Human-made illumination sources have utilized many different technologies to produce light and therefore have a wide variety of CRI values. A sample of commonly used lamps and their CRI values are listed in the chart below.
| Color Rendering Qualities of Commonly Used Light Sources | ||||
| Light Source | CRI | Spectral Strength | Spectral Weakness | Efficacy (lm/w)* |
| Incandescent | 95 | Yellows, Oranges, Reds | Blues, Greens | 15-20 lm/w |
| 2700K Warm White LED | 85 | Yellows, Oranges, Reds | Blues, Greens | 90 lm/w |
| 4000K Neutral White LED | 85 | Blues, Greens, Yellows | Reds, Oranges | 95 lm/w |
| 5000K Cool White LED | 85 | Blues, Greens | Yellows, Oranges, Reds | 100 lm/w |
| ‘Full Spectrum’ Fluorescent | 85 | Reds, Yellows | Greens, Blues | 50 lm/w |
| 4000K Neutral White LED Street Lights | 75 | Blues, Greens, Yellows | Oranges, Reds | 150 lm/w |
| Coated Metal Halide Street Lights | 75 | Blues, Greens, Yellows | Reds | 50 lm/w |
| High Pressure Sodium Street Lights (sepia tone) | 25 | Yellows, Some Orange | Blues, Greens, Reds | 70 lm/w |
| * Efficacy is lumens/watt delivered by a light fixture using this source, the above is approximate | ||||
You can see below how Spectral Power Distribution (Blue to Red) affects color rendering:
Color Rendering Index (CRI) is the only universally accepted method for comparing how different light sources render color. However, in addition to CRI, the relative spectral strength and weakness of a particular light source also have a significant impact on how accurately that light source renders color. Various light producing technologies create more energy in certain portions of the spectrum of visible light and less in others. For instance, most LED sources use a blue LED chip covered by a layer of phosphors to create white light. They generally emit more light in the blue portion of the spectrum, thereby rendering this color more vivid than others. On the other hand, incandescent sources are generally stronger in the red and yellow portions of the spectrum. An example of this difference in spectral strength and weakness is lighting in bathrooms. High CRI warm white LED lighting is generally preferred in residential bathrooms, particularly around mirrors, because the high red and yellow content tends to make one’s skin look vibrant and healthy; whereas sources with strong blues and greens are great for plants but cause one’s skin to have a washed out, greenish-gray cast. The above chart provides spectral strengths and weaknesses of some of the most common lamp technologies used in buildings, although LED is now the preferred source for new construction and renovation.
Studies have shown that color can indeed have an effect, significant at times, on the way a person feels in a space and their overall mood.
With proof of the power of color, it is clear that selection of light sources is about much more than the quantity of light they produce. When considering how a space should look and feel, choosing the light source(s) that renders the colors in that space most accurately is as important as the selection of the colors themselves.
– Blair Malcom, PE, LEED AP
Blair is a Licensed Professional Engineer, a LEED Accredited Professional, and RH’s Director of Lighting Design.