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I wouldn't call it money wasted. There are going to be teething issues with any new technology. Some money will be spent finding out what works best. You're basically paying to learn here. It happened when diesel locomotives replaced steam, when cars replaced horses, even when incandescent lamps replaced candles. It's better to spend a little extra to work out the bugs with new technology if that technology offers significant advantages, than to just continue with the status quo. I also live in NYC, and have seen some LED traffic lights with dead clusters (but not a lot by any means, and it's mostly the pedestrian signals, not the traffic signals). I don't consider this a major issue. Some of these LEDs were installed 5 or 6 years ago. Just the fact that they're still working at all is good news. The lamps they replaced last 2 years on average. Moreover, when the incandescent lamps failed, that part of the signal went completely dark. At least when the new LEDs fail, it's almost always just a portion. What remains on is enough to safely control traffic until the signal can be replaced. There have also been many millions of dollars saved in power costs. Additionally, the LED signals allow the operation of traffic lights off batteries for several hours during a power failure. This was just plain not possible with the older incandescents.
I have a difference of opinion. Look at the coverage area on teh ground in the picture above. The LED luminaire is starting with less foot candles (based on that picture). When diodes start to go out, that's even less. I do agree that LPS/HPS shouldn't be used in street lighting. IMO, Kelvin and CRI should have been considered. Just because the efficacy is high, doesn't mean it's usable lumens in that instance, because of the low CRI. ~165 watts would have been better used with MH150's and controlled optics. If that was being used, I think there would be less people that think LED would be a better choice (in regards to a 'visual' standpoint). Unfortunately, it's not even being considered as an option given todays "green is above all else" society push.
Yes, I noticed that, and it underscores exactly why 5mm LEDs have no place in streetlighting. Besides the degradation issues, I've yet to test any which are much over 80 lm/W. It seems all the R&D is going to power LEDs, which is a good thing anyway as the packaging is superior to indicator-type LEDs.
Efficacy unfortunately was the only criteria used when sodium vapor lights were chosen. At the time (mid 1970s) we really didn't know that much about color rendering, apparent brightness, or how spectral output affects safety. Besides the aesthethics of sodium vapor being poor (my opinion although it seems many on these forums agree with that assessment), its apparent brightness is lower for any given amount of photopic lumens. Many people in NYC in the 1970s complained about the streets looking dimmer when the sodium vapor replaced mercury vapor, even though the claimed output was about the same. On top of that, sodium vapor lights have been shown to kill peripheral vision in studies. This makes it decidedly unsafe for lighting roads. At the time sodium vapor started to be used, there really weren't any viable alternatives which had higher efficacy than the old mercury vapor. I think MH only started to come into its own in the 1990s (at least that's when I remember them replacing sodium vapor in parking lots). So we really could have switched our streetlights over to MH about 15 years ago if we wanted to. For whatever reason we didn't. LED streetlights, if applied properly, offer a much greater lifetime potential than MH. In fact, if you underdrive the LEDs you could possibly get the lamp life to match the fixture life (50 to 200 years, depending upon design). Even if we manage only 60,000 hours, that's still a factor of 3 better than other technologies. While efficacy is important for streetlighting, lamp life is probably even more important to municipalities. IIRC it costs over $100 in labor alone to change out a lamp. In light of this, LED streetlights can easily recoup their costs just based on that. If they offer higher efficacy than alternatives, then it's a bonus.
Again..I agree withya blasterman.
I also respectfully disagree with this part of your post. Only because those claims have yet to be proven. LED"s have not been around long enough to know their true life expectancy in a commercial setting like this. Also, LED's have yet to be put through any federal regulations or standards. Many of LED's have a 'claimed' efficacy rating and real world independant studies are showing that they are vastly over exhaggerated.
