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What Does 415 nm and 660 nm Mean?

When it comes to light therapy for acne and other conditions, some websites throw around very scientific sounding terms that can be intimidating to normal people. A couple of these are 415nm and 660nm. Those terms simply define the color of the light as follows:


Term Scientific Definition Simple Meaning
415nm Visible electromagnetic radiation with a wavelength of 415 billionths of a meter. (a specific shade of) The Color Violet
660nm Visible electromagnetic radiation with a wavelength of 660 billionths of a meter. (a specific shade of) The Color Red.

The sun emits an absolutely tremendous amount of energy, generally called electromagnetic radiation or the electromagnetic spectrum. This energy travels to earth in waves, and the wavelengths are measured in meters.

Most of the sun's energy (radiation) is harmful to us (gamma rays, x rays, most of the UV rays), but the majority of that is blocked by our atmosphere. Some of this tremendous energy, however, reaches Earth, and we call the visible portion of this energy “light.”

The wavelengths of visible light are tiny, ranging from 400 to 700 billionths of a meter. A billionth of a meter is called a nanometer, or nm.

White light, as you likely know, contains all the colors of the rainbow. A specific color can be defined by a range of tiny wavelengths, in nanometers, or nm, like this:


Color Wavelength
violet 380–450 nm
blue 450–495 nm
green 495–570 nm
yellow 570–590 nm
orange 590–620 nm
red 620–750 nm

Quite simply, “415nm irradiation” is violet light, and that’s really all there is to it. Calling it “radiation” makes it sound potentially dangerous and expensive, but “radiation” is just energy (in this case, light energy), and it’s not dangerous or expensive. In fact, it’s life-sustaining and it’s free. If you step outside into the sunlight (always avoid sunburn), you will be bathed in 415nm and 660nm light. That may be one reason your acne improves in the spring and summer months. Another reason may be the Vitamin D produced when the sun bathes your skin.