Hmm... When I was out today I saw some LED traffic lights. These are lights with LED's instead of normal light globes. It is interesting to look at the economics of Traffic Lights, normal and LED.
Firstly, lets look at power consumption. A standard intersection has four lights pointed in each direction. Each of these would be 60-100W. Lets assume that they are all 100W right now for the ease of the maths. So there are 16 lights on at any time. Oops, I am wrong. There are another eight for pedestrians. So we have a total of 24 lights on at any time, out of a total of 64 lights(16 * 3 + 8 * 2 = 64).
Assuming that a set of traffic lights runs 24 hours a day ( and most do) and ignoring the computer inside, this adds up to 2400W 24/7. Assuming electricity is 10c / KW/h, this comes to about $5.76 per day. Lets just round that down to $5.48 for simplicity. Multiplied by 365 days, this comes to $2000 per year for electricity to run the lights. Hmm, that is not cheap. LED Lights have got to be cheaper to run than that.
Assuming that LED's draw 10W per globe instead of 100W, the saving are incredible. So rather than costing $2000/year they now cost only $200/year in electricity. A huge improvement.
But that is not the main reason for replacing globes with LED's. Lets keep looking. Most globes have a 5,000 hour life. The orange is rarely on, so we can ignore it at the moment... The RED and GREEN are equally as probable to have on. So on average, a globe will fail after 10,000 hours in service. This sounds like a lot, but it is not as there are 8,000 hours in a year. Lets assume that they are using some advanced techniques to get 12,000 hours out of each globe. Now, there are 16 main globes (ignoring the pedestrians) meaning that a globe will blow about six times a year. Twelve times a year is a lot!
Lets think about the cost of this. You need to send a team to replace the globes. A team of two might be able to work about 1200 hours a year, and replace one globe every hour including getting set up, and then moving to the next job. At $50K/year each, with a 2.5* multiplier, they cost about $250K per team of two, in order to replace 1200 lights. This comes to about $208 per globe.
That means replacing lightglobes in each traffic light will cost about $2500/year!
Moving to LED globes means that if an LED fails, it does not need to be replaced. It is only when a large number of pixels fail that they need to be swapped out. This is probably after at least 10 years when they would be wanting to do other maintainence anyway.
So, lets compare the costs. Normal lights cost $2000 in electricity, and $2500 in repairs each year. LED lights cost $200 in electricity a year, and $0 in repairs each year. I am guessing that each LED 'GLOBE' costs $30, so the increase in cost once off would be $30 * 64 or about $2000. You can save more in six months with LED traffic lights than standard globes.
3M have just released 
