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A Light Source of a Different Color

Most of us have heard the story of a football team painting the visitors’ locker room pink to calm the other team down 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 has a tendency to calm, and orange can bring out one’s nurturing side.

Since color is actually just a certain wavelength of light that is reflected from a surface back to the eye, the nature of that light can have a significant impact on how we see 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 better a light source renders color. Sunlight contains the most energy across the full spectrum of visible light and is the best light source to render color. Thus, the sun has a CRI of 100. Man-made light sources use many different technologies to produce light and therefore have a wide variety of CRI values. A sample of some of the most commonly used lamps and their CRI values are listed in the chart below.

Light Source CRI Spectral Length Spectral Weakness
Incandescent 95 Reds, Yellows Blues, Greens
Warm White Fluorescent 55 Yellows, Greens Reds, Blues
Cool White Fluorescent 65 Yellows, Greens Blues
‘Full Spectrum’ Fluorescent 75 Reds, Yellows Greens, Blues
Clear Metal Halide 60 Blues, Greens Yellows, Reds
Coated Metal Halide 75 Blues, Greens, Yellows Reds
High Pressure Sodium 25 Yellows, Some Red Blues, Greens


The Color Rendering Index 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, standard fluorescent sources generally emit more light in the blue and green portions of the spectrum, thereby rendering these colors more accurately 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. Incandescent lighting is generally preferred over fluorescent lighting 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 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 today.

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.

– Michael J. Lee, PE, LEED AP

Michael is a Senior Project Manager, Licensed Electrical Engineer, Lighting Designer, and LEED Accredited Professional. Please feel free to contact Michael for further details regarding the above information.