Why do LEDs need heat-sink?
1 W of electrical energy can produce about 683 lumens at 555nm. The white light being a spectrum, 400 lumens per watt is considered as the maximum efficiency. The early LEDs were producing only about 2-5 lumens per watt – the present high bright single chip LED produces 90-110 lumens. The following table gives an idea of the lumen efficacy of various lights.