Color and Vision


Electromagnetic energy radiates out from the sun in waves. These radiant energy waves are of varying frequencies, or lengths. Short wavelengths can be smaller than a billionth of a meter. Very long waves, like radio waves, can be as long as a kilometer. The range of these waves is called the electromagnetic energy spectrum. The human eye can only detect a very small portion of these wavelengths, called the visible spectrum, ranging from 380nm to 760nm.


Gamma xray ultraviolet visible infrared microwaves radio & television waves

The lining of the human eye, the retina, is considered to be part of the brain. It is a complex nerve structure containing photoreceptors that are light-sensitive, and are responsible for translating incoming light into electrochemical nerve impulses. Because of how they are shaped, these receptors are known as rods and cones.

Rods, which are slow-responding, function in low light and are responsible for night or low light vision. These rods are sensitive to the absence / presence and intensity of light energy, but don't distinguish color. Rods number around 600 million per eye, and are located primarily on the periphery of the retina - notably absent from the area of the fovea, where the optic nerve connects to the retina.

Cones, which are rapid-responding, contain photo pigments, which are light-sensitive chemicals. These photo pigments contribute to the sensation of color. The cones are sensitive to the different wavelengths, which the brain interprets as variances in color. These wavelengths, in their pure form, represent the colors red, green, and blue. Varying combinations and intensities of these wavelengths are interpreted as secondary colors by the brain, allowing extremely subtle color distinction. There are far fewer cones in the retina, around 6 million per eye.

Cones, however, are located primarily in the foveal area (with some "blue" cones scattered in the periphery) - and this is the area where the main 2% of our focal field is concentrated - where our critical vision occurs. This means that Cones - the rapid responding, color-distinguishing photoreceptors - are in the best location to serve our vision needs. THUS THE HIGHER THE CRI OF THE LIGHT SOURCE (or percentage of the visible spectrum delivered by the source), THE MORE CONE ACTIVITY, AND BETTER VISUAL ACUITY.

Artificial light sources are compared to sunlight (not "daylight", which can vary with weather conditions, sun angle, etc) with what is called the Color Rendering Index (CRI), a metric indicating the percentage of the visible spectrum delivered by the source. For example, sunlight is 100CRI (that is, it contains all the visible spectrum). Incandescent light is also 100CRI, although it's chromacity curve is rather jagged as opposed to the smoother curve of sunlight. Older warm-white & cool-white fluorescent sources are rated 62CRI, a poor color rendering choice, as it only contains 62% of the visible spectrum. Standard metal halide is about 65CRI (not much better), and high pressure sodium is 22CRI - a very limited portion of the spectrum (mostly yellows).

T5 comes standard in 85CRI, which means that we are using 85% of our eye's potential to see. This translates to 25% better visual acuity than standard MH, and 75% better than HPS.