How can a light bulb produce different colours of light?
In: Physics
Your question is sort of unclear, but I’m going to summarize some of the other answers: it depends on the kind of bulb.
* For incandescent bulbs, i.e. the ones with the filament, you can just color the glass. You do this by putting minerals into the glass before you blow the bulb.
* For “neon” lights, you do this by changing the gas that inside. I don’t really have time to explain stimulated emission at the moment, but if electrons are people in a stadium, they can only move to certain rows. Those rows correspond to colors of light, and we can use those colors to identify the element. Look up [spectroscopy](https://simple.wikipedia.org/wiki/Spectroscopy) if you’re interested (that’s the simple entry).
* For LED bulbs, we can only make one color at a time. This again has to do with quantum properties of the material, just like neon lights, but is complicated by other factors in solid-state physics. Suffice it to say that most “white” LED bulbs are actually composed of three LEDs in the primary colors of light (red/green/blue), not just one white light. So if you can active these with different amounts of power, you can change the color of the light that comes out, from orange (red+green) to purple (red+blue) to pink (lots of red, almost as much green and blue) to almost anything.
* side note: lasers come in different colors for a mixture of reasons that involve all three of the things I mentioned
If you’re asking why different white lights look different, it’s because the amounts of red, green, blue, and the other colors they produce are different. LEDs have more blue light, incandescent more red light, halogen more blue light, etc. I don’t really know how to demonstrate this effect other than to have you look at the spectra (which are continuous instead of discrete like “neon” lights), so I’ll link them [here](https://www.comsol.com/blogs/calculating-the-emission-spectra-from-common-light-sources/).
If these two weren’t your question, feel free to clarify.
src: I’m an astrophysicist and former optical physicist.
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