Why blue lights?

Ever wondered why Backstage lights are always blue? Here is the explanation!

back to school

I promise I won’t go too deep into physics but to understand the “blue-light-answer”, we need to check out a few basics, some of you (definitely me!) might have missed in school:

Our eyes have several photoreceptors, which allow us to perceive electromagnetic radiation between approximately 380nm and 780nm wavelength. In normal words: we can see colors ranging from purple to red – as in a rainbow! Any light waves (~colors) outside this spectrum remain unnoticed. Our eyes simply won’t see them.

day-vision

However, even inside our possible spectrum, not all colors are equally perceived. Green and yellow, for example, naturally seem brighter to us than red and purple. The latter need more intensity to appear in the same brightness. This principle is called the “luminosity function”.

Are you still following? We’re almost there!

night-vision

We just learned that our eyes are most sensitive to colors around green and yellow (approx. 570nm). But as if it wasn’t enough, this condition changes at twilight: The whole curve shifts towards shorter wavelengths, aka. blue tones. That means, if we want to see clearly with little light in dark surroundings, we should use wavelengths around 470nm (= blue) instead of green. Our eyes can see them best at night.  

win-win setting

Consequently, it makes sense to use blue frequencies for (dark) backstage areas because they appear the brightest – the same reason why police lights are blue! But in a theater surrounding, there is another bonus: As the audience is looking towards a bright, well-lit stage, their eyes are in day-mode. Now, please have a look at the curves again: which colors are the LEAST noticed during the day? You guessed it: blue-tones! Conclusion: Not only can we see well backstage with blue, but the light is also hard to see for the public—two birds with one stone.

Thanks for thinking this through with me. I hope you’ll look at the lights differently from now on.

By the way, this is an excellent pub story when you are out with performers and techs. Let me know their reactions. And, of course:

Stay positive and focused!

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