Why do light bulbs have a vacuum inside?

Answer 1

It is something that takes out the oxygen so it can last longer.

A vacuum is a negative pressure, meaning there is no oxygen in there. Most modern bulbs don't use a vacuum. They simply pump in an inert gas that won't contribute to burning, and that chases the oxygen out.

Answer 2

So the filament lasts longer. Because oxygen in the bulb would cause the hot metal elements to oxidize and burn out.

However, modern light bulbs don't actually hold a vacuum. Instead they are filled with an inert (electrically non-conducting) gas such as Nitrogen. An inert gas is used to fill the bulb (instead of just pumping out almost all the ordinary air to leave a near-vacuum) because the action of filling the bulb with an inert gas flushes away ALL of the ordinary air. In addition the inert gas has the very useful physical property of helping to conduct heat from the glowing filament to the glass bulb. This allows the whole surface area of the glass bulb to radiate heat into the surrounding air. It is important to understand that the inert gas does not allow the filament to "burn away" as it would if some air were still present in the bulb. This sometimes happens if a light bulb gets knocked and gets even a tiny crack in its glass bulb: the oxygen present in ordinary air will quickly make the filament burn away. So, to summarize, the inert gas which is used to fill the glass bulb allows the filament to glow very brightly without burning and conducts the heat produced by the filament away to the glass bulb.

Answer 3

Glass is an insulator used in a light bulb.