How do you know that not all of the electrical energy used by a television is transformed to sound and light?

Not all electrical energy used by a television is transformed into sound and light because some energy is lost as heat. This can occur in various components, such as the power supply and circuitry, where resistance leads to energy dissipation. Additionally, efficiency ratings for televisions indicate that a percentage of energy is not converted into usable output, confirming that some energy is inevitably wasted.