Page Content 1. UT Extension serves the citizens of Fayette County with educational programs in the areas of Agriculture, Family and Consumer Sciences, Community Resource Development, and 4-H Youth Development.
A large globe light, like around a vanity mirror, that is rated at 25 watts consumes exactly the same amount of energy as a small refrigerator light bulb also rated at 25 watts..  Size as a power ratingThe wattage rating of a light bulb is directly proportional to energy consumed by that light bulb. A light bulb rated at 60 watts consumes 50% more energy than a 40 watt light bulb.
Power capacity is how much energy is stored in the battery. This power is often expressed in Watt-hours (the symbol Wh). A Watt-hour is the voltage (V) that the battery provides multiplied by how much current (Amps) the battery can provide for some amount of time (generally in hours). Voltage * Amps * hours = Wh. Since voltage is pretty much fixed for a battery type due to its internal chemistry (alkaline, lithium, lead acid, etc), often only the Amps*hour measurement is printed on the side, expressed in Ah or mAh (1000mAh = 1Ah). To get Wh, multiply the Ah by the nominal voltage. For example, lets say we have a 3V nominal battery with 1Amp-hour capacity, therefore it has 3 Wh of capacity. 1 Ah means that in theory we can draw 1 Amp of current for one hour, or 0.1A for 10 hours, or 0.01A (also known as 10 mA) for 100 hours.