What’s A Watt Worth?

While attending my friend Henry’s house party recently, I was disappointed to find that not only did he not read my blog, but he also didn’t use LED lighting around the house! With an annual cost per watt calculation, I calculated that he was losing hundreds of dollars each year on the bollard lights lining the walkway to his house.

Using only 15w, today’s most efficient LED equipped reflector bollards have 80% luminaire efficiency and produce 800 lumens. The metal-halide lamps and ballasts around my friend’s house require 70w to produce 816 lumens—with only 24% efficiency! To put it simply, the bollards emit about the same amount of light, but the LED version uses 80% less energy.

If Henry keeps his bollards on for eight hours a day for seven days a week, it would cost $0.44 a watt each year. Twelve bollards equipped with 70w metal halide lamps and ballasts would be about $370 in energy costs. On the other hand, twelve 15w LED bollards would only cost $80. For every year Henry delays switching to LEDs, he loses $290!

But why do LEDs use so much less energy? Because of their small size, LED chips provide directional lighting, whereas metal-halide lamps emit light in many directions. The majority of the light in my friend’s metal-halide lamps was trapped inside the reflector-style bollards wasting most of the light. LED chips can direct all of their light at the reflector, which means they’re using most of the light originally produced. Less wasted light means less wasted money.

 After I gave Henry a hour long lecture on the savings of LEDs (it was a really fun party),the next time I visit him , I expect to find a walkway lined with LED bollards. Calculate how much money you’re losing each year by using an annual cost per watt chart and researching energy costs in your area. Do you think it’s time to switch to LED?

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