Question

The glass of a lit 75-watt incandescent bulb is hotter to the touch than the glass of a 25-watt compact fluorescent (CFL) bulb that emits the same amount of light. What could be a reason for this

Answer 1

Incandescent bulbs have very low efficiency when compared to other types of bulbs, as they only transmit 5% of their given energy as useful light. This also means that 95% of the energy is transferred into stores we make no use of.

CFL bulbs on the other hand are 7-10% efficient and thus need less Watts to supply the same light to that of the aforementioned bulb.