What is blue light?

Question

What is the "blue light" often discussed in relation to human melatonin production, sleep/wake cycles, etc.? A Google search seems to define it as light of a particular wavelength, suggesting that it literally means "light that's blue in color," but many articles seem to attribute blue light to the light emitted from computer/TV/etc. screens, which is not inherently blue in color.

What exactly is blue light? For example, would adjusting the "blueness" of a colored light bulb, as if raising and lowering the "B" slider in an "RGB" color selector (raising "B" in the morning and lowering "B" in the evening), have at least a hypothetical positive impact on human circadian rhythms?

Answer 1

Blue light means wavelengths that appear to the human eye as blue when they are presented alone. This light is important for sleep/wake cycle regulation because this is the wavelength that cells that participate in this regulation respond to.

"White light" is light that covers the full visible spectrum; sunlight, for example, is fairly white. However, that light contains plenty of blue light as well as all the other colors - there is no actual wavelength for "white," it is a collection of all the other wavelengths.

Similarly, TVs and other screens emit red, green, and blue light. Because of our makeup of photoreceptors, this is sufficient to mimic any visible color. When referring to the blue light of televisions, people are referring to that blue component. If you disabled the blue channel somehow you would get a very strange picture but also activate less the cells that sense daylight based on blue light.

The reason screens are so problematic is that people stare directly at them and take in a lot of light. Other sources of bright, whitish light would have the same effect.