Dave's powertrip #8: Are we being LED to a brighter future?

LED lightbulb

My best childhood friend was visiting one summer evening. We were in my bedroom planning our night of astronomy when all of a sudden the bedroom light went out. I did not think much of it beyond the inconvenience of replacing the bulb. My friend, on the other hand, was shocked to find out that a light bulb could burn out. It turned out that my friend had lived for 12 years in a house that was once owned by the town purchasing agent. The purchasing agent had installed light bulbs that were used in traffic control and were meant to last, so he had never seen a light bulb stop working. In my childhood home, you could pretty much expect that some light bulbs would burn out three or four times a year.

Light bulbs are not something that I give much thought to until they stop working. We have a couple of light fixtures in our house that have a problem with bulb life. One particular fixture has six bulbs arranged in a line. The number four position is the short-life socket with an average life of less than six months. The fixture is located in the master bathroom with the number four position a little over four feet above the sink on my wife’s side of the room. I did a little research on what shortens a bulb’s life. The typical answers are vibration from fans or air-conditioning, heat, and resistive sockets. In this case, I suspect that it may be the socket.

This brings me to our topic of LED lighting. Earlier this year the US Department of Energy released a paper titled “Life-Cycle Assessment of Energy and Environmental Impacts of LED Lighting Products.” This particular release is “Part 1: Review of the life-cycle energy consumption of incandescent, compact fluorescent, and LED lamps,” and was updated in August of this year. This is one of the most comprehensive studies of lighting I have come across.

The study introduces a parameter for comparison based on 20 million lumen-hours. This comes from an estimate of the number of lumen-hours produced from a single 60W LED replacement bulb over its expected life. The study also projects LED bulb performance in 2015 as shown in Table 1. The estimated life time for the incandescent bulb is a little shorter than our household experience, except for that number four socket. The other surprise is the 2015 prediction. A doubling in efficacy, lumens / watt, is aggressive to me – especially when you consider that it comes with 60 percent increase in operating life.

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Dave FreemanPower to the people!

-Dave Freeman