White is a color that is often taken for granted, but it has some interesting properties when it comes to hue. By definition, white light contains all wavelengths of visible light equally. This means that white has no specific dominant wavelength, and therefore no distinct hue. However, there are some nuances to the hue of white that are worth exploring.
The nature of white light
White light can be created by combining red, green, and blue light – the three primary colors of light. This is known as an additive mixture. When red, green, and blue wavelengths combine in equal amounts, we perceive the result as white.
However, white light can also contain other wavelengths besides RGB. Sunlight is composed of a continuous spectrum of wavelengths, including those our eyes perceive as color, as well as ultraviolet and infrared wavelengths we cannot see. When all these wavelengths strike our eyes in roughly equal amounts, we see sunlight as white. Other light sources like incandescent bulbs also emit a continuous spectrum that appears white.
So while white contains the RGB primary colors, it is not exclusively composed of them. This will become important when discussing the hue of white.
White objects and reflected light
When discussing the hue of white, it also helps to consider white objects, rather than just white light. A white object, like a white wall or paper, appears white because it reflects back all wavelengths of visible light more or less equally. While the illuminating light source contains the full spectrum, the white surface reflects this full spectrum without absorbing some wavelengths more than others.
This is what gives white objects their “neutral” color quality – they do not skew the hue by selectively absorbing certain wavelengths. Compare this to a red object, which absorbs most of the spectrum and selectively reflects back the red wavelengths.
The blackbody radiation curve
| Temperature (K) | Appearance |
|---|---|
| 1000-2000 | Red |
| 2000-3000 | Orange |
| 3000-4000 | Yellow |
| 4000-5500 | White |
| 5500-8000 | Blue white |
When objects are heated, they begin to emit light – this is known as blackbody radiation. As temperature increases, the peak wavelength of this emitted light shifts. There is a continuous spectrum of radiation that correlates with temperature.
At lower temperatures, in the 1000-3000K range, blackbody radiators appear red, orange, or yellow. As temperature increases to 4000-5500K, the radiated light appears white to our eyes. Above 5500K, the light begins to take on a blue tint.
This illustrates an interesting point – white light can lean towards subtle color tints while still being considered “white.” This brings us closer to defining a hue for white.
Defining a dominant wavelength for white
As mentioned previously, pure white light has no single dominant wavelength. By definition, it contains roughly equal amounts of all visible wavelengths. However, given that blackbody radiators demonstrate how white light can take on subtle tints of color, we can explore the concept of a dominant wavelength more closely.
Within the range of 4000-5500K temperature that appears white, we can break things down further:
| Temp (K) | Dominant wavelength |
|---|---|
| 4000 | 450 nm (blue tint) |
| 5000 | 550 nm (green tint) |
| 5500 | 590 nm (yellow tint) |
Here we can see that within the range of white light, there are subtle shifts in dominant wavelength that introduce tints while still looking white.
So while white has no single dominant wavelength, we can define small hue ranges for different white light temperatures.
White index and chromaticity
Another way to quantify the hue of white light is through color temperature and chromaticity coordinates on the CIE 1931 color space.
The white point, or neutral reference, is located at the center of the chart:
| x | y |
|---|---|
| 0.33 | 0.33 |
This point represents pure white light, at around 5000K temperature. Differences in temperature and tint can be plotted relative to this white point.
For example, a warm 2700K white light may have coordinates of:
| x | y |
|---|---|
| 0.4476 | 0.4074 |
While a cool 6500K white light may have coordinates of:
| x | y |
|---|---|
| 0.3127 | 0.3291 |
The x and y coordinates indicate subtle shifts in hue away from the neutral point while still appearing white. This numerical specification of chromaticity is another way to define the hue of white light.
Impact on materials and perception
As we have seen, white light can take on subtle tints while still being considered white. These small variations in hue can have an impact on how materials and objects are perceived.
Warm white light with more yellow/red content tends to make objects appear brighter and more vivid. Cool white light with more blue content can make objects and materials appear cooler and more muted.
This effect is purely subjective perception – the physical properties of the objects have not changed, only the hue of the illumination. This demonstrates the subtle power of white hue on material appearance.
Natural white balance
Our eyes and brain automatically adapt to the color of the lighting environment – this is known as white balance. Over time, we learn to perceive white objects as white, regardless of the lighting conditions.
Indoors under warm, incandescent lighting, a white wall still appears white because our visual system filters out the warm, yellowish tint. Outdoors under cool blue daylight, that same wall still appears white, as the blue tint is filtered out.
This adaptation means the subtle hue shifts in different whites are often imperceptible to us. Our white balance corrects for the ambient light, preserving the constancy of object color. This allows white to take on a range of subtle hues across contexts.
True hue vs tint
This brings us to an important distinction around the hue of white – the difference between true hue and tint.
As discussed, white light can take on subtle tints based on temperature that make it appear warmer or cooler. However, these are not true hues in the sense of the spectral colors. There is no wavelength of “white” light – white is the sum of all colors.
The tints come from small imbalances in the light, not from the presence of a true spectral wavelength. So while we can measure and quantify the tint, white does not have a true hue in the same way as other colors. The tints are a side-effect of the continuous spectrum that makes up white light.
Conclusion
In summary, while white has no distinct hue, it can take on subtle tints based on the temperature and chromaticity of the light. Warm white tends to have more yellow/red tint, while cool white picks up more blue tint. These tints induce subtle perceptual effects on materials. However, white has no true hue due to containing all wavelengths – the tints are just imbalances in a complete spectrum. Our white balancing mechanisms allow white to maintain its neutrality across lighting conditions. So white does not have a hue in the strict sense, but exhibits nuanced tints depending on the source and environment.
