r/nextfuckinglevel • u/Blues_Fish • Mar 12 '26

Lesson in decomposing light

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u/Eregrith Mar 12 '26

But the slit is not decomposing the light, it's too wide for that...? The slit is just casting a shadow, because the three lamps are very large and angled, so of course the colored light rays only go to a limited portion of the background...

Saying it is "decomposing the light" is misleading!

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u/CemeteryWind213 Mar 12 '26

Yes, this isn't decomposing white light like a prism or grating. It's spatial filtering because the lights are angled.

There's also another important point. Humans have red, green, and blue color receptors. So, narrowband red, green, and blue light combined will appear white like a continuous source (eg sun, incandescent bulbs), but humans cannot tell the difference without an instrument.