From Guest Blogger Daniel: A Bright Future for Street Lighting
Over 50 years ago, an exciting new light source emerged and was quickly put to its first practical use in vehicle indicators. Nowadays, the light emitting diode (LED) is put to widespread use, from television remotes to aircraft landing lights right down to the fairy lights which adorn the neighbourhood this Christmas. The popularity of LED lighting has grown as people become more environment conscious, due to its high energy efficiency and long lifespan, not to mention the incredible array of colours now available.
However, it seems that only within the last few years have governments been considering and installing LED lights on our streets. This is surprising considering the long standing knowledge of their advantages which, added to the stress on available fuel resources and global aims to limit the human impact on climate change, make LEDs a leading option for public bodies wishing to show their commitment to a sustainable future. Now this all sounds very eco-warrior but the fact remains that an LED street light has numerous advantages over the traditionally used sodium lamp and as a few large cities across the world (mainly in the UK, Canada and USA) embrace this alternative light source many people are seeing the benefits for themselves.
Any person who has approached a big city after dark, be it by road, rail, sea or air, will have noticed the orange glow arching over the urbanised region, most notable on a cloudy night. This is produced by the sodium street lamps which emit light in all directions and have created the phenomenon of ‘light pollution’, adding to the other unnatural emissions of large metropolises. The nature of these traditional street lights also creates uncomfortable levels of glare for motorists and pedestrians alike, indicating another area where LED street lighting can improve mobility around urban areas at night time. An LED lamp reduces glare by projecting light directly down onto the street, and provides a brighter clearer light which improves visibility for drivers and cyclists, meaning safer roads at night-time. They also provide immediate illumination so there is no ‘warming up’ period when the streets are not sufficiently lit.
Further to these practical benefits, the environmental and economic advantages are also great. LED lights are extremely energy efficient, using about half the power for the same output, and have a much longer lifespan of up to 60,000 hours per bulb (the equivalent of 16 years when illuminated for 10 hours a day), five times longer than traditional street lamps. These aspects of LED street lamps have made them an economically viable option for numerous large cities to try out, including New York, Dallas, Seattle and, quite surprisingly, the smog soaked Los Angeles.
However, there are a few disadvantages for these cities to consider before committing themselves to a full-blown changeover. The high initial cost of installing LED lights can be off-putting, but it should be seen as an investment, since the energy savings will eventually see the costs repaid. A trial in Bath, England, predicts an eight year period to earn back the installation expenses, which in terms of human history is not a daunting time frame. Additionally, the directional nature of the lights can limit the illumination of sidewalks, so some extra configuration may be required to spread the light for pedestrians benefit. Overall, these issues can be easily overcome with the help of a government committed to a brighter future for towns and cities aiming to save energy and create safer streets.
From the article:
“A trial in Bath, England, predicts an eight year period to earn back the installation expenses, which in terms of human history is not a daunting time frame.”
Payback time is a very primitive method to evaluate investments. Better methods are discounted cash flow and internal rate of return. How LED lights would compare with high pressure sodium lights on that basis I don’t know, but that information should be made available. If the internal rate of return is less than the interest rate, then probably it would make more economic sense for municipalities to invest the money elsewhere, perhaps by improving the energy efficiency of buildings.
Also, the directional advantages of LED lights are at best questionable. Here in Albuquerque, the traditional high pressure sodium street lights, which are insufficiently directional, are gradually being replaced with directional high pressure street lights. Reflectors make them directional.
I am not opposing replacing high pressure sodium street lights with LED street lights. I am simply pointing out that the article lacks sufficient information to make a rational decision.
I would point out that there is not a significant efficiency penalty between high pressure sodium and LED lighting. That’s simply not true.
LED lighting is directional, so you don’t take a penalty in the light being absorbed by a gradually dirtier and dirtier reflector… but otherwise the lumens/watt are quite similar at the intensity levels the streetlights would use, with sodium likely showing slightly higher efficiency (LED’s become more efficient the lower the power level that is applied, and less efficient at greater power levels, for a street light they are going to be turned up about as high as the diodes can handle, and hence far less efficient then lab demonstrations).
The big gain is the lack of labor in maintenance. It costs A LOT for a team to drive out and replace a bulb… I believe most cities merely replace whole streets worth of working bulbs on a periodic schedule; and with the 5-fold longevity of the LED lights, that schedule could be dramatically reduced. In regions that require an 8-year payback (I agree with Frank that there are far better evaluation techniques), my suspicion is that they are still employing the crews to do SOMETHING, and just not swapping out bulbs as often. The only way real savings could be seen via the LED route is if you dramatically reduce the number of people working the crews… so there are other issues attached to this.
My suspicion is that LED’s will gradually lead to far greater illumination of cities, with higher-quality whiter light, and there will be similar, if not a net greater amount of night-time energy consumed as a result.
That said, I love LED’s, as I find the light to be beautiful, and it’s good for the soul to walk through the night in well-lit streets or streets lit with bright colors. So while I don’t think this will be a remarkable benefit to the environment, I do welcome it.
(note that any place where traditional incandescent bulbs are replaced by LED’s there is a TREMENDOUS advantage for the environment, but city street lighting usually doesn’t entail traditional incandescent bulbs).
In some cities, the incandescent bulbs used in traffic lights have been replaced with LEDs. That may not seem significant, but it turns out that the traffic lights at some intersections use more than 5 KW of power when they are incandescent, so it really is significant. The high power consumption is partly the result of using long-life bulbs which are inefficient. Unfortunately, LEDs in that application are not completely problem free.
Incandescent traffic lights generate enough heat to melt snow and ice off of the lenses, which LEDs cannot do, so there have been problems with the lights becoming obscured with snow and ice. It may be that traffic lights designed from the ground up for LEDs could circumvent that problem, perhaps by using hoods around the lights. Or, they could use electric heaters which would be activated only when needed.
It may be that LED lights will eventually replace all other types of lights except perhaps in situations where lighting is needed only occasionally and briefly, such as in closets.
Frank,
I was only discussing the option of switching from high-pressure sodium bulbs to LED’s.
I have no problems with the concept of switching stoplights from incandescent to LED. The stoplights in many places have already switched to LED – because the lower cost of maintenance makes the ROI on such a switch yield far higher than 100%.
I think that concern over ice sticking to the bulb is more or less a non-starter. In the regions where such a concern might find merit, you could simply have a glass cover that is slightly inverted LED’s do generate heat, and they are easily destroyed by the heat they generate… so often the new stoplights would simply have a few colored diodes on the surface of a highly thermally-conductive surface, so the generated heat cannot build up. But slipping a glass cover over such a bulb would produce more than enough heat to keep ice from building on the surface of the glass, and if the surface is slightly inverted there would be little-to-no snow adhesion.
Of course, that would mean that work crews would have to go to every intersection of the city and slip a glass cover over the streetlights in the autumn and remove that cover in the spring (lower ROI from the switch)… but for incandescent bulbs they have to replace the bulbs more often then that anyway.
In most cases, winter storms that could cause problems are likely rare enough that it’s worth just not worrying about them, and increasing the brightness of the LED’s to such a point that they could be seen through ice or snow during the winter, then perhaps dimming them (single-point citywide dimming controls are possible) in spring, summer, and autumn for greater energy savings.
Glenn,
I realize that you were mainly concerned with street lighting, but since LEDs are used also for traffic lights, it seemed relevant.
I grew up in Wisconsin and Minnesota. Under some weather conditions, the heat emitted by LEDs is insufficient to keep the lenses clear of ice and snow; the problem has actually occurred and is not simply theoretical. In about 1962, the temperature in Minneapolis stayed below zero degrees F for about two weeks. That was unusual, but it’s not unusual for the temperature to be too low for several days in a row for the minimal heat from LEDs to keep the lenses clear. That would be especially true for the amber light, but sometimes they use LEDs for only the red and green because the amber is on only briefly.
Quite often snow is more horizontal than vertical, so changing the lens angles would make little difference. People in the frozen north sometimes have to scrape snow and ice off of the side windows of their cars; glass covers on traffic lights would similarly become covered with ice and snow.
No doubt in most of the country, iced traffic light lenses would not be a problem and I’m sure that there are solutions. But sometimes changes are made before there is adequate thought given to complications and how to prevent them; that’s a widespread problem that covers more than lighting.