Metamerism and why paints color shift
Metamerism and Why Does Paint Color Shift
By John Shearer
Surprisingly, it may not be your eyes, and the fix might require nothing more than a change of light bulbs. What’s happening is metamerism, and it can affect any color at any time, day or night, indoors or out.
There’s No Such Thing as Color
There really isn’t. That’s because what appears to be a certain hue is nothing more than reflected light. Anyone who has tried to distinguish red from blue in the dark of night soon finds that it’s impossible. Without light, color simply doesn’t exist. However, there’s even more to it. The type and quality of that light can appear to change any color vastly from what you may have thought it was before.
Is it the Fault of the Paint Store?
It happens to everyone eventually. Despite the number of hours spent in front of the paint display, the color finally chosen is almost certain to be quite different by the time it reaches the buyer’s home. Either the paint store has made a terrible mistake, or the color has changed inside the can. Is either of those things even possible?
Lighting Makes a Difference
Paint stores, particularly the big-box variety, generally prefer to light their environment with fluorescence, and there are good reasons for that. For one thing, it provides a good general illumination, and for another, the practice has a more benevolent effect on the company’s bottom line. Although fluorescent light causes few problem in most cases, it’s a different story where color is concerned,
The fact is that every different light source contains its own distinctive combination of color frequencies. Some colors are more sensitive to the effects of these frequencies than are others, and these are the ones most likely to fall victim to metamerism.
Since fluorescent lighting tilts toward the bluer end of the spectrum, it can cause particular problems with the reds. That’s why the beige that was perfect when chosen at the paint store can turn almost pink on your living room wall.
Fluorescent light is not the only culprit. Every light source has its own particular ambiance. Consider, for instance, the fact that:
- Incandescent light imparts a warm yellowish tint.
- Halogen light burns bright and cool.
- Daylight bulbs emit a cool, bright light to mimic the great outdoors.
- White fluorescent lighting is extremely cool.
- Full-spectrum bulbs are the closest possible to neutral.
On the other hand, the effects produced by compact fluorescent lighting can vary widely. As these bulbs gradually replace the incandescent variety, manufacturers are making every attempt to appease the public by providing them in a wide range of color temperatures.
Light and Color Temperature by Kelvin
A more scientific approach relies upon a system of measurement to evaluate the relative warmth or coolness of different sources of light. It’s known as the Kelvin rating, and the lower the number, the warmer the illumination.
In general, the measure from warm to cool breaks down as follows:
- The flame of a match measures 1,700 K
- The flame of a candle measures 1,850 K.
- Low-pressure sodium bulbs measure 2,000 K.
- Sunrise and sunset measure 2,500 K.
- Incandescent bulbs measure between 2,700 and 3,300 K.
- Color halogen and daylight bulbs measure between 3,200 and 3,500 K.
- Moonlight measures between 4,100 and 4,150 K.
- Cool-white fluorescent bulbs measure between 4,000 and 4,600 K.
- Bright daylight usually measures between 5,000 and 6,000 K.
- The xenon arc lamp measures 6,420 K.
The Natural Lighting Effect
Some may be surprised to learn of daylight’s position on this list. Although it may seem counterintuitive, the temperature of light on a hot summer day can easily reach a cool 8,000-10,000 on the Kelvin scale.
Another feature of daylight, however, is its tendency to change in temperature throughout the day. Although it will always fall on the cooler side of the scale, you can expect a certain warmth from early morning light that will turn more neutral as the day wears on. By afternoon, a distinct bluish cast will appear, and this will remain in place until dusk. During sunset, a warmer aspect will again predominate.
When Two Colors That Match in One Location Fail to Match in Another
Many have had the experience of bringing a sample of paint to the store for matching only to find that the selection that corresponded so well in the brick-and-mortar no longer does so back at home. When two swatches that appear identical under one light source fall entirely out of synch under another, you can blame it on a difference in their reflectance curves. The factor is present in all objects, and since the human eye can only perceive the color of reflected light, the curve determines which color the eye that observes it will actually see.
How the Reflectance Curve Affects Color Perception
White light contains every color in the spectrum. When it falls upon any solid object, that object will either absorb all of its color wavelengths, absorb none of its color wavelengths, or absorb only some of its color wavelengths while reflecting the others back. The object’s reflectance curve dictates which wavelengths it actually reflects.
The human eye cannot detect any of the absorbed color wavelengths. It perceives only the reflected color wavelengths. A blue object only looks that way because it has absorbed every other color in the light spectrum but blue. White objects reflect the entire white-light spectrum, and this causes the eye to perceive them as white. Black objects, for their part, absorb every wavelength, reflecting back no color for the human eye to detect.
Color Mixing Increases the Effect
The effect of metamerism on any particular color will rise or fall in direct relation to the number of pigments that combine to create it. Metameric failure is most likely to occur with colors in which four or more pigments combine. Paint companies that realize this will make every effort to minimize the effect by keeping their color recipes down to three or less.
The colors most likely to fall victim to metameric failure are those comprised of varying amounts of the three primary pigments of red, green and blue. This includes such variables as:
- Gray and grayish blue.
When matching these colors in particular, it is vital to make the comparison in the light under which they will eventually coexist.
In addition to the light source and the number of pigments used in a mix, any hue can change in relation to the colors that surround it. That’s why the reflected color of a red rug or warm wood floor will often lend a pinkish tint to white walls. While the resulting warmth can sometimes be inviting, a reddish reflected light could also put a dull cast on a light green surface or turn a beige one ruddy.
Any mixture of opposites on the color wheel will gray a color. For example, mixing a red with a green will result in brown. These combinations of reflected light will always mute the color on which they fall:
- Red on green.
- Green on red.
- Blue on orange.
- Orange on blue.
- Purple on yellow.
- Yellow on purple.
The following suggestions can assist in preventing reflected light from wreaking havoc with your paint selection:
- Always choose color in northern daylight or under a full-spectrum bulb while keeping sunlight strictly out of the equation.
- Bring a large sample into the intended room for evaluation as the quality of light changes throughout the day.
- Isolate the color from outside influence by viewing it through a length of PVC pipe or other empty tube.
Observer Metamerism: When Human Color Perception Goes Awry
When two people disagree on a particular color, the fault isn’t always in the light source. A less-appreciated phenomenon, observer metameric failure, can cause two people to perceive an identical color under the same conditions in vastly different ways. In fact, variations in color vision between two individuals are more common than some may realize. The phenomenon can cause a paint chip that looks blue to one observer to appear, for example, distinctly green to another.
Any of the following discrepancies in color perception from one person to another can cause observer metamerism:
- Differences in the light sensitivity of each individual’s color cones and rods.
- Disparities between the proportion of cones receptive to longer versus shorter wavelengths.
- Variations in the number of color cones in the center of the visual field in relation to those that lie in the peripheral region.
The coloration of the lens and macular pigment can also play a role in observer metamerism. Since all light that enters the eye must pass through both before reaching the photoreceptors, the degree of yellowing in either of these two areas can alter an individual’s perception of a particular hue. This is especially common when the coloration is unusually intense.
Geometric Metamerism: When the Angle Makes a Difference
The phenomenon of geometric metameric failure occurs when two colors that appear identical from a certain position no longer match when viewed from another. This discrepancy is a common feature of pearlescent paints, and it is due to differences in the angles at which light reflects off the surface before reaching the eye.
Some have used geometric metamerism to explain occasional differences in color perception between men and women. Those who subscribe to this theory suggest that because men’s eyes tend to be more widely spaced than women’s are, they will view reflected light from slightly different stereoscopic angles and see, as a result, another shade of the same color.
The Material Effect
Light temperature, geometric angle of sight and individual physical characteristics of the observer are not the only things that can influence color perception. Material is another. A color’s characteristics as seen in such varied fabrics as cotton, rayon, nylon, wool and polyester can differ widely from one light to another, even when all have just emerged from the same dye bath. This makes it even more vital to compare such colors in the light under which they will all eventually dwell.
What to Avoid
While it is impossible to avoid the effects of metamerism with equal ease in all situations, there are ways in which to minimize the trouble it can cause. When attempting to match colors, be sure to:
- Make the comparison in the lighting conditions under which the objects will be viewed.
- Double-check the color under at least three different light sources.
- Perform daylight matching in the shade and never in the sunlight.
- Remember that even in the same room, a paint color will appear to slowly morph from one shade to another throughout the day.
- Bring large paint samples home to evaluate the color under varying conditions.
Winning the Battle Against Metamerism
As annoying as metameric failure can be, it is easily conquered. All it really takes is an understanding of what is happening and why. Knowledge is power, and you can take this information to the paint store with confidence that the battle with metamerism is one that you can actually win.