system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some light bulbs need to warm up, while others don't?
gpt
There are a few different types of artificial light in common use, and they all behave differently.

- The good old-fashioned light bulbs are called "incandescent."  They work by making running electricity through a tiny little tungsten wire to heat it until it glows.  These have to be warm to work, but they warm up completely in a fraction of a second, so they're pretty much instant-on from your perspective.  Problem is, they're super inefficient and waste lots of electricity, although we've made some more refined varieties (called halogen) which run even hotter and use a bit less energy.

- Fluorescent bulbs are a newer, more efficient technology.  Both the long, straight tubes in office lights, and the little twisty spiral bulbs at home, use this technology.  They pass electricity through a special gas at low pressure, and the electricity makes that gas glow.  These turn on pretty fast, but don't reach full brightness immediately.  They keep getting brighter gradually over the next few minutes as the gas inside warms up.  These are much more efficient, but some people don't like the gradual warm-up.  They also contain a small amount of mercury, so they're not totally environmentally friendly.

- Vapor lamps are the worst offenders for slow warm up.  It's so bad, they are only used for big lights which stay on for a long time like streetlights,  warehouses, and school gyms.  These work by using an electric arc to vaporize a little blob of sodium, which gets so hot it glows super bright.  The lights take five minutes or more to turn on at all, and then they gradually get brighter over the next few minutes.  That's just how long it takes to heat up the blob of sodium to melt and vaporize it.  The reason we put up with this kind of lamp at all is that they're very efficient.  The most efficient ones, for things light street lights, make a very ugly yellow light, so stores and schools and warehouses use a slightly less efficient type which runs at higher pressure and makes nicer white light.

- A new kind of light is called LED.  These are little semiconductor devices, like computer chips.  They're the most efficient type of all, and can be made into all different shapes and sizes, with all different colors of light.  They also last a very long time (years or decades).  And they turn on *immediately*.  So fast, in fact, that you can turn them fully on, then fully back off again, *thousands of times per second*.  We sometimes use this to our advantage, to dim their output very efficiently by blinking them on and off faster than the eye can see.  The only reason we don't use LEDs absolutely everywhere is that, as a newer technology, they're pretty expensive.  In the coming years, these will likely start to replace all the other kinds above.