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Finally, we’ll evaluate the three common commercial lighting technologies. In this, we’ll go beyond the
scales to provide an understanding of how the color rendering of each is not just measured but
perceived, and how the color rendition of each technology changes over time.

The Human Eye, The Ultimate Measuring Device

The human eye consists of rods and cones. The rods provide our scotopic vision, which is primarily our
night vision, useful in low light conditions but virtually non-existent in our perception of color.
Conversely, the cones provide our photopic vision, which is useful in brighter light and provides the vast
majority of our color perception.

(1)
It is estimated that our photopic vision can differentiate about ten million colors .

Color and White Light

One unit of light measurement is wavelength. The visible spectrum of light is in the wavelengths roughly
between 400 and 700 nanometers (nm). The shorter, higher frequency wavelengths are at the
ultraviolet (UV) side of the visible spectrum while the longer, lower frequency wavelengths lean toward
the infrared side.

Color Violet Blue Green Yellow Orange Red
Wavelength(nm) 400-450 450-490 490-560 560-590 590-635 635-700

Figure 1. Visible Spectrum and Wavelengths

Pure white light is our basis for perfect color rendition. It is the presence, in equal intensity, of all
wavelengths of visible light.

Color Perception

The core purpose of this document is to convey that the human eye can only perceive the specific color
of an object when the wavelength of that color is emitted by the light source. When a wavelength is not
emitted, the related color is not seen.

Example: A ball that is red and green sits in the late morning sun. Both the red and the green
are vibrant because the sun is delivering light across both the red and green wavelengths.

Now, we take the ball indoors, into a light source that is weak in the spectral band between 520
and 540nm (see Figure 1). Since the green wavelength is missing from the light source, the
green colors of the ball are now missing as well; the ball now appears to be red and something
more brown or grey.

Color is also subject to the intensity of a wavelength relative to the intensity of the other wavelengths
present. This is called context. In context, a green will be perceived as being more green when it’s
adjacent red as opposed to a blue. It is only possible to adequately perceive a spectral band in context.

Competitive Analysis, Color Rendering in White Light Page 2