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LED Bulb Update: Beginning to see sign of failure.
It has now been about 4 months since I installed the first of five LED exterior lamps, and this one lamp that has been on 95% of that time is beginning to dim and blue. It's still a reasonable white color, but it has clearly shifted up the color spectrum and is putting out about 1/2 as much light as the others. This became mildly noticeable about 1-2 weeks ago and is now quite clearly degraded from the performance of the newer lesser used lamps.
In terms of energy use, at 3W, it's a clear winner over the 7W incandescent I had been using in that fixture before (don't really need much light there). On bulb cost however, it's a clear loser at 5-6 times the cost for roughly the same service life. So the question is how much of that bulb cost difference we recouped. My knee jerk reaction is 'not much', but I think it's worth doing the math anyway:
Incandescent - .007kW x 120days x 24hours x $0.09/kWh = $1.81
LED - .003kW x 120d x 24h x $0.09/kWh = $0.78
$1.81 - $0.78 = $1.03 in energy savings (so just call it a single buck given the 95% of use during those hours)
So clearly, our overall cost for this lighting is 2-3 times as much as the 7W incandescent with this kind of bulb life. I'm hoping this one lamp is just an early failure, but I suspect it's going to be the status quo. Regardless, end-user monetary cost obviously can't be the only factor to consider with these things.
The LED lamps still cut our outdoor lighting energy use by more than half - even if in this case, a single bulb has saved barely more than 10 kWh. In the case of the remaining 4 lamps however, the energy savings are likely to be roughly double that for each fixture, having replaced 13W fluorescents - or roughly 90 kWh between the lot of them assuming the same MTBF for all if I replace them at half output (or 270kWh/yr). Regardless, it cannot be ignored that a 13W fluorescent puts out a lot more light than a 3W LED, so our ability to utilize this lower power version is limited to outdoor security/safety.
Edit: Just to be clear, these are the Bulbs that Wal-mart has been selling for just under $6 each. No surprises, but it would seem that one gets what one pays for on these.
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