Traffic lights are being converted from incandescent bulbs to LED arrays to save
ID: 2079055 • Letter: T
Question
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 20 mA of current. There are three arrays per light - R, Y, G. A small city has 1560 traffic signals. Since one light is always on 24/7, how much can a city save in one year if the city buys their electricity at 7.2 cents per kWh?Explanation / Answer
Traffic light consists of
Case 1 :- Incandescent lights
Power rating of incandescent light is P = 300 W for each color R, Y, G
Energy Consumed Per year if one bulb on for 24 hours a days i.e either of three bulbs
E = P*T*D = 300 * 24 * 365 = 2628000 = 2628 kWH / year
Cost of energy is C = E * 7.2 = 2628 * 7.2 = 18921.6 cents per year = $ 189.216 / year per traffic signal
Case 2 :- LED
Each array consists of 61 LEDs and Three arrays for each color
Given each LED operates at V = 9 V and draws I = 20 mA
Power Consumed by each LED is P = 9*20*10-3 = 0.18 W
Power Consumed by on bulb P = 0.18*61*3 = 32.94 W
Energy Consumed Per year is E = 32.94*24*365 = 288.5544 kWH
Cost of energy consumed per year C = 288.5544 * 7.2 = 2077.59168 cents = $ 20.7759 per traffic signal
Money saved in for one traffic signal by using LED is $ (189.216 - 20.7759) = $ 168.4401
Total Money saved is 1560*168.4401 = $ 262,766.556 from all traffic signals in the city.
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