Question

why why led is used in tester and not tungsten bulb

plz give me answer​

Answer 1

Answer:

With LED's, a small increase in voltage will result in a large increase in current. So it is really hard to get just the right voltage to keep an LED at the right brightness. If you let the voltage just get a tiny bit too high it may destroy the LED.

What makes it even harder is that as the LED gets hot, the current will also increase. Naturally when you power it up it will tend to get hot. As a result it is just too much trouble to drive an LED with a voltage. Some form of current limiting usually has to be put in place. It doesn't have to be a resistor, but that is probably the most simple way to do it.

LED light bulbs have circuitry integrated into them that overcomes all these problems.

Old-fashioned incandescent light bulbs (including halogen bulbs) are different. The part that lights up is made from a thin tungsten wire that glows when it gets hot. The wire has resistance which limits the current automatically. This resistance is also what causes it to heat up. And, icing on the cake, the resistance goes up with temperature, so incandescent light bulbs are really stable when powered from a voltage source