What exactly is blue light?
Blue light is the shortest wavelength part of the visible spectrum, roughly between 380 and 500 nanometers. It's just light you see, not radiation that passes through your skin, and not an invention of display screens.
White light always consists of a mixture of wavelengths. What you perceive as white, therefore, by definition contains a blue part. The question is never whether there is blue light in it, but how much and at what time of day.
Where does it come from?
By far the largest source is the sun. A cloudy day outdoors still gives you many times more blue light than an evening spent behind a phone at maximum brightness.
| Source | Relative amount | When relevant |
|---|---|---|
| Daylight | By far the largest | During the day, and then beneficial |
| LED lighting | Moderate, varies per lamp | Evening indoor lighting |
| Screens | Small, but close to your eyes | Last hours of the day |
That last column is the whole point. It's not the quantity that makes a screen relevant, but the time of day and the distance to your eyes.
Why do you hear so much about it then?
Because two different discussions are intertwined. One is about sleep, the other about eye damage. The effect on sleep is well-substantiated; for eye damage from screens, it is not.
This distinction gets lost in much marketing, which is precisely where exaggerated claims arise. What is and isn't established about your eyes can be found in is blue light bad for your eyes.
When is blue light beneficial?
During the day, especially in the morning. Bright light with a blue component resets your biological clock, keeps you alert, and actually helps you fall asleep better in the evening.
Anyone who spends the whole day indoors with curtains closed and turns on bright lights in the evening reverses that order. We explain how this mechanism works in blue light and sleep.
What do you do with it practically?
Seek it out during the day and limit it in the last hours. That's the whole rule, and it's more important than any filter you choose.
If you are still behind a screen during those last hours, our SLEEP tempers the part that inhibits your melatonin. During the day, this is not useful, because then that light works for you.
This article is intended as an explanation, not medical advice.
