indoor lights, large display screens, and TV screens. The U.S. Department of Energy estimates that
the widespread use of LED lights by 2027 could result in energy savings of 350 10
9
kW.h.Example 12.7 According to Sylvania, a light bulb manufacturer, its 75 W CFL floodlight consumes 23 W
and produces 1250 lumens. What is the efficacy of the floodlight?Example 12.8 A 100-W CFL light manufactured by Buyer’s Choice, consumes 23 watts and has an illumi-
nation rating of 1600 lumens and service life of 8000 hours and costs $1.81. As an alternative
a generic 100-W incandescent light bulb costs $0.38 and produces 1500 lumens and has a ser-
vice life of 750 hours. Let us compare the performance of each light bulb by calculating the effi-
cacy for each light, and also estimating how much it would cost to run each light for 8 hours
per day for 220 days in a year. We will assume electricity costs 9 cents per kWh.For the Buyer’s Choice 100-W CFL light:
For the generic incandescent 100-W light bulb:
It should be obvious that the CFL light is more efficient and economical to operate than the
generic incandescent.costa
8 hours
day
b1220 days 21 100 W2a
1 kW
1000 W
ba
$0.09
kWh
b$15.84
Efficacy
1500
100
15
costa
8 hours
day
b1220 days 21 23 W2a
1 kW
1000 W
ba
$0.09
kWh
b$3.64
Efficacy
1600
23
70
Efficacy
Light Produced 1 lumens 2
Energy Consumed 1 watts 2
1250
23
54
12.6 Lighting Systems 367
TABLE 12.6 Comparison Between High Intensity Discharging Lights
High Intensity
Discharging Lighting Efficacy Life Color Rendition Color Temp.
Type (lumens/ W) (hours) Index (CRI) (K)Mercury Vapor 25 – 60 16,000 – 24,000 50 (poor to fair) 3200 –7000
(warm to cold)Metal Halide 70 –115 5,000 – 20,000 70 (fair) 3700 (cold)
High Pressure Sodium 50 –140 16,000 – 24,000 25 (poor) 2100 (warm)
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