How can a light bulb produce different colours of light?
In: Physics
The question is a bit complicated to answer so this may not be ELI5.
First: What humans PERCEIVE as color is not necessarily what is being produced by a light bulb. The human eye has 3 kinds of receptors that are sensitive to red, green and blue frequency light waves. Light entering the eye stimulates these receptors by varying amounts. The brain interprets these different level of stimulation as a particular “color”. For example: the color we see as “magenta” actually does not “exist” in the sense that there is no light frequency that is “magenta”. Magenta is perceived when we have blue and red combined. (Blue and red light frequencies are on opposite ends of the visible light spectrum)
Second: A light designed to produce different colors may have more than a single light emitting device. Basically by doing the reverse of what our eyes and brains do, it can fool the brain into thinking it is seeing a spectrum of colors.
Third: some lights are designed to emit different colored lights of a single frequency range. These can either be through the selection of the right metals or gases (the explanation is DEFINITELY NOT ELI5) or by passing the light emitted through filters or phosphors which will modify the frequencies that are emitted from the light source. Filters generally just block some light frequencies (therefore changing the perceived color) while phosphors will absorb light energy of a certain color and emit light of another color.
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.
For some light bulbs there are electronics inside supplying power to three different colored smaller “bulbs” that when applying varying power will shine brighter or dimmer. When these three colors are mixed with different ratios they can produce basically all colors. For classical bulbs you can use different materials for the light emitting wire and gas and glass and you are able to get slightly different colors as well.
Latest Answers