Question

energy can neither be created nor be destroyed .then why we say that "switch of the lights otherwise the electricity get wasted "??

what wasted means ?
how it will get wasted as energy can neither be created nor be destroyed

Answer 1

physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time.[1] This law means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another. For instance, chemical energy is converted to kinetic energy when a stick of dynamite explodes. If one adds up all the forms of energy that were released in the explosion, such as the kinetic energy of the pieces, as well as heat and sound, one will get the exact decrease of chemical energy in the combustion of the dynamite. Classically, conservation of energy was distinct from conservation of mass; however, special relativity showed that mass is related to energy and vice versa by E = mc2, and science now takes the view that mass–energy is conserved.

Conservation of energy can be rigorously proven by Noether's theorem as a consequence of continuous time translation symmetry; that is, from the fact that the laws of physics do not change over time.

A consequence of the law of conservation of energy is that a perpetual motion machine of the first kind cannot exist, that is to say, no system without an external energy supply can deliver an unlimited amount of energy to its surroundings.[2] For systems which do not have time translation symmetry, it may not be possible to define conservation of energy. Examples include curved spacetimes in general relativity[3] or time crystals in condensed matter physics.

Answer 2

Wasted doesn't mean that the energy is destroyed.... It's just converted to non usable or less usable forms.

Eg- when u burn a candle, the chemical energy gets converted into heat and light energy which basically can't be converted into chemical energy again.

In ur case, power converts into light energy n a bit of heat energy which become unusable. Hence u r asked to turn of lights whn not in use

Hope that helps:))