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.
The energy stored in a battery, called the battery capacity, is measured in either watt-hours (Wh), kilowatt-hours (kWh), or ampere-hours (Ahr). The most common measure of battery capacity is Ah, defined as the number of hours for which a battery can provide a current equal to the discharge rate at the nominal voltage of the battery. The unit of Ah is commonly used when working with battery systems as the battery voltage will vary throughout the charging or discharging cycle. The Wh capcity can be approximated from the Ahr capacity by multiplying the AH capcity by the nominal (or, if known, time average) battery voltage. A more accurate approach takes into account the variation of voltage by integrating the AH capcity x V(t) over the the time of the charging cycle.