This course is part of the Interiors Academy

Both natural and artificial lighting have a profound impact on how we perceive color. This course will provide the reader with a foundational understanding of how we perceive light and color and of the three characteristics—correlated color temperature, color rendering index, and spectral power distribution—which describe the quality and color of light. This course will also include a brief overview on the composition of paint and colorants, and explain how qualities such as sheen impact how the selected color is perceived in the space. Finally, this course will explore how light creates more than just visual effects; it also has biological and psychological effects that can impact the health and wellbeing of occupants. Included in this content will be research on design psychology as a basis for making informed color choices for clients, in addition to writing paint specifications that help avoid color discrepancies and confusion.

Photo courtesy of Benjamin Moore & Co.

The type of light that illuminates a room or surface greatly impacts how we perceive the color.

THE SCIENCE OF LIGHT

It might seem an obvious statement, but without light, there would be no color. Less obvious, perhaps, is the impact that certain types of light have on the colors we perceive. Think about how a human face appears when illuminated by early morning light. No matter what the color of skin, it will appear warm and soft. That same face in the midday sun will be marked with harsh, contrasting shadows, and the skin tones will appear “cooler.” Now imagine how that same face appears when bathed in candlelight versus a conventional fluorescent fixture. While candlelight is kind to most of us, under the fluorescent fixture, human skin often takes on a sallow, greenish cast.

The colors we perceive are determined in part by the quality and quantity of the light that illuminates them, whether natural, artificial, or a combination of both.

For millennia, humans relied solely on the sun or firelight. Today, of course, artificial lighting illuminates our world, day and night. We lived with the incandescent, or Edison bulb, for over 100 years. Today, several types of artificial lighting systems, each with its unique characteristics and impacts on color, illuminate our buildings. Light-emitting diodes, or LEDs, are quickly replacing other types of lighting in both new and existing buildings.

Because light has such a profound impact on color perception, design professionals should have a foundational understanding of how lighting choices will impact paint color and finish selections. To do so, we must first look at the nature of light itself.

The Electromagnetic Spectrum

Light is composed of many wavelengths of energy. The full range of these frequencies is called the electromagnetic spectrum. Only a small portion of these wavelengths are visible to the eye. This narrow band is known as the visible light spectrum, and it includes all the colors of the rainbow.

Photo courtesy of Benjamin Moore & Co.

Additive mixing (left) involves the mixing of light where the resulting color will become lighter and eventually white. Subtractive mixing (right) involves the mixing of substances and results in a darkening of colors.

The visible light spectrum includes wavelengths ranging from 780 nanometers down to 390 nanometers (nm). For comparison, UV light ranges from 10 to 400 nm, and X-rays are shorter still. Specific wavelengths correspond to specific colors. Reds have the longest wavelength and range from 650 to 700 nm. “Cooler” colors have shorter wavelengths. The violets have the shortest wavelengths of all and range from 390 to 430 nm.

Warmer, longer wavelengths are easier to see in dim light, while cooler colors tend to disappear. This concept is important to remember when we discuss the impact of light on paint color.

Two Ways of Making Colors with Light

When a beam of light is projected onto an object, the object will absorb some wavelengths while reflecting others. For instance, a red object absorbs all but the red wavelengths. However, it’s not always that simple. For example, an object may appear yellow if the object absorbs blue light but reflects green and red light, because when these wavelengths mix, they create yellow.

You can create different colors by mixing light in what are called the “primary wavelengths” of red, green, and blue. This is called additive color mixing.

Mixing red and green produces yellow, while mixing red and blue yields magenta, and mixing green and blue yields cyan. Mixing all three primaries creates white. Color televisions, computers, and other displays rely on additive color mixing to create the full range of colors.

Another way to create colors is through subtractive mixing. You likely recall the thrill of using tempera paints to make new colors—for instance, mixing blue and yellow to create green. This is subtractive color mixing. Most materials, including dyes, paints, colorants, and inks, rely on this process.

Most design professionals are familiar with the color wheel. Based on the primaries of red, yellow, and blue, this tool uses subtractive color mixing to create a plethora of secondary and tertiary colors. White and black can be added to create a nearly limitless number of tints and hues. The printing process, which relies on inks, uses slightly different primaries of cyan, magenta, and yellow, but this is still a subtractive process which relies on the mixing of substances, not on the mixing of light.

Photo courtesy of Benjamin Moore & Co.

How the Eye (and Brain) See

Whether color is created through additive or subtractive color mixing, the way we see and process color is the same. To better understand the relationship between color and light, let us first recall the basic biology of the human eye and how the brain interprets information received by it.

The eye works very much like a camera. A transparent cornea allows light to enter the eye, and the iris controls the amount of light entering through the pupil. The cornea and lens work together to focus the image on the retina, which is located at the back of the eye.

The retina—comparable to the film, sticking with the camera analogy—is lined with light-sensitive receptors called rods and cones. These photoreceptors convert light into electrical signals, which are transmitted to the brain via the optic nerve. The visual cortex of the brain converts the image impulses into objects.

The human eye has far more rods than cones—about 125 million rods to 7 million cones. Each type of receptor plays a distinctive role in vision. (The retina actually contains a third type of receptor, which does not play a role in vision, but which is essential for regulating the body’s circadian rhythms.)

Rods primarily perceive light and dark, and they are more sensitive to dim light than cones. Hence, rods are especially important for night vision. Rods are far more sensitive than cones, and better at detecting motion.

Cones detect colored light. The human eye contains three types of cones: red, green, and blue. Each is sensitive to a different range of wavelengths. Many cones are located in the fovea, a small pit in the back of the eye that helps us perceive sharpness and detail.

The color of the objects we see is largely due to the way the objects interact with light, and how that light is ultimately reflected or transmitted to our eyes. Using the example of the yellow object above, if an object transmits green and red wavelengths, the green and red cones are stimulated and we see the object as yellow.

Photo courtesy of Benjamin Moore & Co.