An energy efficient light bulb uses 15 W of power for an equivalent light output of a 60 W incandescent light bulb. How much energy is saved each month by using the energy efficient light bulb instead of the incandescent light bulb for 4 hours a day? Assume that there are 30 days in one month.

5400 W-hr

Explanation:

Given:

Power used by energy efficient bulb = 15 W

Power used by incandescent bulb = 60 W

Total time of bulb used = 4 hours/day * 30 days = 120 hours

Now,

Energy used by the individual bulb by using them for 120 hours

we know,

Energy = Power * Time

thus,

Energy consumed by energy efficient bulb = 15 W * 120 hour = 1800 W-hr

Energy consumed by incandescent bulb = 60 W * 120 hour = 7200 W-hr

hence, the energy saved will be = 7200 - 1800 = 5400 W-hr