LEDs are popping up everywhere and these street lights are just another sign that the technology is really starting to become mainstream. We just purchased some solar lighting for our outside gardens and guess what, they are all LEDs. Now I'm just waiting for some good sunny days to see if the LEDs really burn brighter than traditional lighting. I'll keep you posted.
Beth, the laptop I am using now had LEDs for backlighting for the disply. It helps the battery last much longer. LEDs in this application replace EEFL lights, which are fairly effecient compared to incandescent.
As the price comes down they will replace other types of bulbs. Just the much longer lifetime helps. Even at home, not having to replace bulbs is a plus. For something like streetlamps bulb replacement is a very costly thing. This is a good trend.
Beyond the cost barrier, what have the downsides been for a broader array of LED applications? I've run into plenty of downsides with CFL lights, which frankly aren't compelling enough to justify the added expense and the potential energy savings.
Beth: Incandescents have long been optimized to work on our common 110V power supplies, and therefore need no extra circuits to adapt the input source to the output. LEDs are more complicated. With an LED, you need to understand the input source and its variability. On the output side, you need to understand optical requirements and the amount of lumens you want to generate. All of this will be worked out over time, though, as more LED apps pop up.
Incandescent replacements have some fantastic advantages. I recently replaced the landing light in my 172 with an LED lamp. The constant vibration and heat make incandescents a poor choice for the cowl mounted landing light location in older Cessna's, but that's the only technology that was available at the time. Considering the promise of greatly improved life and a current draw that's nearly 1/10 of the original, the LED lamp was an ideal choice. Since the landing light only pulls a couple of amps and has such great life, I leave it on all the time.
The only disadvantage I've seen to incandescent replacements is the waste heat from traffic lights. Now there's not enough heat to melt the snow off here in blustery Chicago.
Charles, I agree that LEDs are cost effective and energy saving light sources, which are best suited for in-house and office purposes. But is it that much powerful for replacing the sodium vapor lamps in streets? If that’s the case, a considerable amount of energy can be saved.
Good question, Mydesign. Cree claims that its LED models can serve as direct replacements, in terms of performance, for a 70W high pressure sodium vapor lamp, a 150W high pressure sodium vapor lamp, and even a 200W high pressure sodium vapor lamp, but we have no quantitative data to support that claim.
tekochip's comment about melting snow is right on the money. Although streetlights, being down facing, may not be as serious, I've seen the problem with stop lights being covered with snow which is something I had never seen before.
My other question about LED's relates to the advantage of not having to change them as often. Unfortunately, my experience with LED based technology is that they don't "burn out" as more common lights do. What is going to happen if the streetlights get dimmer and dimmer? When is it going to be a dangerous situation and what will the trigger be for getting someone up there to change it?
The technology is out there to count the number of hours a fixture has run, then turn it off when it reaches its (non-catastraphic) end-of-life.
Here's where LED Street lighting can get REAL interesting when it comes to impacting the bottom dollar. The technology is also to a point where the streetlights talk to eachother and a central computer over a WAN. Then, when one fails, it will create a work order telling city/utility/property manager where the problem is, and what the problem is. No longer do workers have to drive around looking for street lights that aren't working at 10pm. Pretty interesting stuff.
The technology I speak of is from Juno Lighting Group. I had a lunch and learn on this stuff and it's pretty cool. There are testing reports from every mfg that will indicate what the usable life of the LED is (LM-79) which is calculated in hours. Juno's "Lumen Depreciation Indicator" counts to 50,000 hours on their fixtures, then turns on a little indicator under the trim when the usable life is approaching. When it reaches the end of life, the can will actually turn off. Then, the user can press and hold the button to reset for an additional 5,000 hours up to 2 or 3 times... to buy a little bit of time. (don't quote me on the numbers there, but the theory is correct) I just sell the stuff!
Also, when it comes to handling the problem of Lumen depreciation, Lithonia Lighting's LED Troffer's have an option that actively manages the lumen output over the life of the fixtures so as to maintain constant lumen output over the usable life of the fixture.
This is how it works: When you wire up the fixture for the first time, the system drops the output and therefore wattage down to 80% of output. (Design Lumens) Then over the life of the fixture the system will bump up power consumption to always maintain Design Lumens. The user won't notice any lumen depreciation over time.
Now, as for how you would know you've reached end of life? Not an option on this particular fixture. As far as how this relates to LED Street Lighting, The LED are just a semi-conductor. The technology is there. Just need to move it to that platform.
I've been told power companies drive around looking for lights out, maybe that's not true. But waiting for someone to call and tell you that a light is out isn't very pro-active either.
LED Street Lights have gained ground and are being implemented right here in Stamford and Greenwich CT. LED lighting is certainly the wave of the future. However, only by educating the public to the true savings of LED bulbs will they become commonplace. The initial cost can sometimes seem high. It is only after comparing the cost vs savings over time do you see the real benefit of LED lighting solutions. I commend all cities and towns that are reducing costly energy consumption by utilizing energy efficient solutions.
Why is it nothing in the article speaks to the bottom line. Efficiency, usability and durability. Sodium lights can have efficiency of 200 lumens/watt. LEDs have 100. See wikipedia.
LEDs have wideband, selectable wavelength. Sodium is narrow, harsh and often color-blinding.
Newest LEDs and arrays have unproven durability and must be housed properly to account for icing conditions.
Not showstoppers but definitely considerations. A recent energy survey of my mom's residence resulted in all incandescent bulbs replaced with slow, low-lumen CFLs 18 months ago. I have since reverted half of them back to hot, quick-on, high watt and useable halogens. Solar arrays on the roof keep her feeling green. Not one size fits all for LEDs either. LEDs work great for landscape and atmosphere lighting. For handiwork and reading, give me a big bright soft-white every night or day.
As engineers and designers, we need to stop chasing fads and letting marketers yank us around. Just the facts, ma'am, just the facts.
Another issue is from the Astronomy community. Light pollution is an ever increasing problem. The spectrum from low pressure sodium lights can be filtered out. Can the white light from the LEDs be filtered or will we never see the stars again?
The energy saving of the LED streetlights is impressive. We had a different issue with LED parking lot lights. Unlike the incadescent lights which were too hot for bird nests, the LED lights did not have same heat which allowed a good spot for birds to nest. With no solution from the manufacturerer, we returned the lights for credit and re-installed the old lights. This was a while ago, and I hope that this potential problem has been addressed.
While the LED lights certainly do save a lot of power and energy, they have the potential to save a lot of money in maintenance costs as well. Hopefully the market for street lighting is a bit less cost sensitive, allowing the use of better quality and higher reliability components, so that the support electronics will outlast the LED portion of the assembly. I would certainly like to never need to climb up and change another sodium vapor lamp bulb again.
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