Chapter 1, Problem 1.20P

Traffic lights are being converted from incandescent bulbs to LED arrays to save operating and maintenance costs. Typically, each incandescent light uses three 100-W bulbs, one for each color R, Y, G. A competing LED array consists of 61 LEDs with each LED requiring 9 V and drawing 20mA of current. There are three arrays per light—R, Y, G. A small city has 1560 traffic signals. Since one light is always on 2417 , how much can a city save in 1 year if the city buys their electricity at $7.2\cancel{c}$ per kWh?