I came across a question: Four bulbs with different power rating, bulb A (240V, 40W), bulb B (110V, 36W), bulb C (12V, 60W) and bulb D (6V, 0.5W) are connected to relevant power sources. Which bulb is the brightest. At first, i thought the highest power will be the brightest. But the answer is bulb A and the explanation gave is it gives the most energy. Why is that?