Question

Tell the substance present in LED

Answer 1

 Light-emitting diode (LED) contains mainly Ammonia and Hydrogen in it.
It is often small of small size. Its working principle is Electroluminescence.
They have many advantages like-  lower energy consumption, longer lifetime,  smaller size, and faster switching.But it is also expensive.It was invented by 
Oleg Losev ,
James R. Biard  and,
Nick Holonyak 

Answer 2

LED = Light emitting diode
It is a type of lamp which needs less electric energy to glow.It is because it contains hydrogen(H2) and ammonia(NH4) in it.