Hi. You’re here. That means you’re likely confused by HSL. You might know that H-S-L stands for: hue, saturation, and luminance, but what do the these different attributes mean? Well, first, let’s take a step back and ask ourselves…
What is color?
Technically speaking, color is a function of different types of light. Everything in the world we see, we can see due to the existence of light. Light arrives in the form of an electromagnetic wave, and the range of visible light comprises only a small percent of the full spectrum of electromagnetic waves. The human eye can generally detect only the wavelength range between 390nm and 700nm.
How does the human eye distinguish between different colors? The human eye contains three types of cone receptors that each detect a different wavelength range. Of the three cone cell receptor types, the first (L) detects red, and its most sensitive point is 565 nm. The second (M) detects green, its most sensitive point being 535 nm. The third (S) detects blue-violet, and its most sensitive point is about 420 nm. Note: A woman was discovered recently who possesses a 4th cone cell receptor type that allows her to see tens of millions of colors more than the average human.
If, when a beam of light enters into the the human eye, (S) cone cells record the strongest response, and the other two cone cell receptor types record almost no response, then the brain will know that the light entering our eyes is blue-violet. Based on this, we can distinguish a variety of colors.
Therefore, the three primary colors we talk about in photography (Red, Green, Blue) are not the physical properties of light, but based on the unique physiological characteristics of the human eye to determine.
It is worth mentioning that the sensitivity of cone cells is extremely strong, almost a photon can stimulate the cone receptor cells, and so the human eye can also be observe in relatively dark outside environments.
Through the above knowledge, we have learned this: that color is essentially different wavelengths of light into the human eye, and that people have unique visual perception.
The “H” in HSL stand for Hue. What is Hue? Hue can be notoriously hard to define, but basically, it refers to the degree to which the color represents its primary feature. In other words, it refers to “the redness” of red.
The “S” in HSL, Saturation, indicates the “intensity” of a given color. The higher the saturation of a color, the more vivid it is; the other hand, the lower the saturation of a color, the closer it is to gray.
The “L” in HSL: Luminance
What is luminance?
Luminance refers to the “brightness” of a given color. This is the way that colors are divided into light and dark, such as light blue and dark blue. Different colors naturally have different distinguishing levels of brightness, Yellow brightness, for example, is relatively high, while purple lightness is relatively low.
For any given hue, then, there is a saturation, and luminance. Given the hue red, we can establish the saturation (i.e. bright red) and luminance (i.e. dark red).
Hue and Emotions
It is no secret that different hues have been used since the dawn of artistic expression to evoke different feelings. Red, for instance, evokes passion and activity. Blue is often used to denote a stark, quiet feeling, and purple has been traditionally used to create an air of majesty or mystery. In post-processing photography, we can use these emotional cues to our advantage. For example, this photo, edited two way, can be used to expressed either a warm sunset atmosphere, or a cool dawn atmosphere. In either case, hue plays an important role.
This article should have helped you become familiar with the three attributes of HSL (hue, saturation, and luminance), what they are, and a bit about how they can be used to generate a specific emotional impact.
This marks the end of this episode of our Photographer’s guide. See you soon next time and receive update by following Pixel Magazine.
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