Since I am in the utility business I will stick my two-cents in. If you are using a regular old incandescent bulb, 40 watts max is the way to go so it doesn't overheat and burn the lens. But, from an amount of light standpoint, don't go by watts, use the lumens rating. So if you are using cfl, or led, look at the amount of lumens...higher the number brighter the light. Higher the number the "whiter" the light will be. Conversely, the lower the number of lumens the "warmer" or more yellow/softer the light will be.
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