The architecture of light: architectural lighting design concepts and techniques. A textbook of procedures and practices for the architect, interior designer and lighting designer pdfdrive com

Figure 6.6 All rods are sensitive to light in the same manner. Thus, they translate only a value judgment.
THE TROUBLE WITH WHITE LIGHT
This science needs to be most thoroughly considered as it relates to so-called “white light.” With the advent of modern, highly-engineered electric light sources, we have harnessed technology that allows us to create light sources that can appear as a pleasing version of neutral when viewed directly, yet render colors very poorly.
Figure 6.7 shows that if we create a light source that emits just the right
wavelength of “blue” light and just the right wavelength of “orange” light, our cones will send a three-digit number to our brain that will be translated as neutral.
Figure 6.7 The perception of neutral from a light source can be created through a combination of as few as two wavelengths of light.
Figure 6.8 The perception of neutral light is more commonly the product of a wide variety of visible wavelengths.
What is inherently dangerous is that when our brain detects a “neutral” light
source, we are tempted to believe that this light source will accurately render all of the potential colors in the environment around us. But if we created the light source illustrated in figure 6.7, it would accurately render only two colors; the rest would be muddled and gray. We would successfully have created a source that appears perfectly neutral to the eye, but renders only oranges and blues. For this reason, a designer should avoid describing light as simply “white.” To speak accurately of light sources, we must discuss two distinct properties:

• The completeness of the spectrum of a light source or “Color Rendering Index,”
• The balance of spectrum of light source or “Color Temperature.”

Chapter 7 The Color Science of Light Sources

Like all color experiences, “white” or neutral, is relatively subjective, and people may experience it slightly differently. In addition to the variation in individual color sense, there are two other factors that contribute to “white” being a dangerous term to label a light source.
The first of these factors is a simple physical shortcoming of
photoreceptors. Our cones rely on chemical photo-pigments to cause the chemical reaction that translates vision. When we exhaust the supply of photo- pigments the cones can no longer “vote.” This temporary exhaustion is called “bleaching” of the photoreceptors and is the reason that after staring at a saturated color for a long period of time, we see the “inverse” of a color when we look away.
The second shortcoming is based on our brains’ habit of ignoring
repetitive information that it deems of little use. Your brain is a device of efficiency, and if it feels that a repetitive signal is being ignored, it will stop sending it. In this manner, as you stare at an object, your brain grows bored of telling you that the object is colored. The brain starts to ignore the signals sent by your eye, and your perception of the object’s color begins to shift towards neutral. More appropriately, your brain is deciding that the color of that object is the “new white,” and, thus, every other color is judged from it.
These factors together mean that an object appears to be most saturated
with color the instant we look at it, and fades as our cones run out of photo- pigment. This subjectivity also means that we can do much arguing about the color of an object or light source. We have already pointed out that we can eliminate argument about color by labeling individual colors by their corresponding wavelength. Here we are interested in applying this simplicity to light sources. We specifically care about the light sources that we rely on to reveal the colors of the world around us. In an attempt to limit confusion and argument, we insist on describing two unique properties of every light source: Color Rendering Index and Color Temperature.