Why so few streetlights are LEDs driven by SMPS?

Hello,
The commercial "SMPS driving LEDs" fraternity dont want anything to do with the street light market because of the need to give a 10 year warantee, and the rough outdoor environment, plus the £60 charge whenever one fails from a big mains transient etc, because somebody has to get the cherry picker out.

Is this why eg Philips, Tridonic, GE etc are not into streetlights using LEDs powered by SMPS?

In our local park, the streetlights are dometic CFL's in a fancy enclosure. Over the UK, most streetlights are not LED, but are sodium based tubes...horribly inefficient

Well observed. That's exactly the situation. Someone, either manufacturer or the maintenance organization has to keep them running so they go for the lowest overall running cost rather than best technical performance.

Consider a typical UK street light: Ambient temperature range from say -20C to +90C (cold winter night to hot summer day) although it wouldn't need to switch on at high temperature, it's own running heat could easy reach 90C. Now take an average 'lights on' period across the year of 12 hours per day, that equates to about 4,380 operating hours per year. Now look at the expected lifetimes of typical electrolytic capacitors as used in SMPS. Obviously you design defensively with expectation of capacitance dropping over time but to guarantee 10 years (43,800 hours) of fault free operation over such extreme conditions is beyond most companies risk level.

Sodium lamps are actually very efficient by the way but being monochromatic causes problems, especially to security cameras because they make it impossible to distinguish different colors.

Brian.

Thanks, another point that i suspect is the case with streetlights in UK at least, is that the government dont even know if they want them at all.....and so dont want the expense of an SMPS driven LED streetlight, as they may be turning them off in a few years time.

I am fortunate to live where there are very few street lights. I can look up and on a clear night see the milky way and thousands of stars. To be honest, I wish they were all turned off except for safety critical spots.

I figure it's illegal to drive around with defective car lights so why do we need street lights as well. For pedestrians, it would be cheaper to buy them all flashlights than pay for a few days of street light electricity, let alone the lights, poles and cables as well.

I don't buy the security aspect, at least in most cases, I figure it's easier to spot a criminal with a flashlight in the dark than John Doe appearing to innocently pass by why eyeing the place for a break in.

Brian.

Now look at the expected lifetimes of typical electrolytic capacitors as used in SMPS. Obviously you design defensively with expectation of capacitance dropping over time but to guarantee 10 years (43,800 hours) of fault free operation over such extreme conditions is beyond most companies risk level.

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I agree 100%; it is the electrolytic capacitors that are the culprit. And the voltage spikes are the next.

But I do find it amusing that they shamelessly advertise 10 year life - some advertisements even say 15 years (I certainly will not be able to take them to the court after 15 years).

Not only sodium lamps are more efficient than mercury lamps, the human eye is more sensitive in the yellow green range and that makes the sodium lamp appear brighter for the same light output.

Also people are very shy to tell the actual light output vs the total energy input. LEDs produce lots of heat anyway (that is what it feels).
Sodium lamps are actually very efficient by the way but being monochromatic causes problems, especially to security cameras because they make it impossible to distinguish different colors.

Brian.[/QUOTE]

treez said:

Hello,
The commercial "SMPS driving LEDs" fraternity dont want anything to do with the street light market because of the need to give a 10 year warrantee...

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why you think that 10 year warrantee required?

Velkarn said:

why you think that 10 year warrantee required?

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Good questions often do not have good answers. Perhaps the idea for a 10 year warranty came in some obscure file first put up by some clerk in some departments. It simply went unchallenged.

If it runs for 2-3 years without any problem, it is very likely to last their full life, i.e., 10 years. Probabilities can be calculated exactly but the cost of replacement may be far more than the cost of the lamp set after 5-10 years.

It is also very likely (probabilities cannot be calculated) that some one in the next 10 years will order that the lamp posts are looking ugly and need replacement with carbon fiber based poles. - or something similar.

Or some new technologies will take over.

In fact, the same company may suggest to the same government for the replacement of their old lamps with their newest baby. Cost be damned.

But the 10 year warranty is very important for the file to master past the audit. Public faith is rather delicate.

why you think that 10 year warrantee required?

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Thanks, yes in UK, the local councils wont buy it unless there's a ten year warantee.

treez said:

Thanks, yes in UK, the local councils wont buy it unless there's a ten year warantee.

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I do not know about the UK but usually they are used in conjunction with a maintenance contract. That takes care of cost...

and what about electrolytic-capacitor-less shemes? i saw some...

As dimming isn't required and reliability is paramount, I wonder if regulations are actually counter productive and a simple polypropylene (or similar reliable 'dry' dielectric) and a simple bridge rectifier isn't sufficient. Given the fixed load presented by the LEDs, if PF is a problem it can be corrected with a series inductor or even a circuit copied from a fluorescent tube could be adapted - without the starter of course.

I've returned from 9 days away today and due to long traveling time had an overnight stop in Exeter, a city in south west England. Last night I went for a walk along the River Exe on a path that crossed several LED lit bridges. Most of the lights worked fine but some were dead and very annoyingly, some were working like strobes, flashing off and on about once a second. It was hard on the eyes and I could see how epilepsy could be triggered in vulnerable people. In all cases where they had failed, all the LEDs in the luminaire were either always off or were flashing simultaneously so it had to be a PSU fault causing the problem. I didn't notice any instances where some LEDS were working and others weren't in a single unit.

Brian.

Thanks, please dont answer as i dont want to waste your time, but i wish i could ask you more on that...like did you notice how many leds roughly were in one , or any of the lamps, and the basic size of the led area, and the overall shape and color of it, so i could see if i could identify it.

It took 6 hours to get home from Exeter via Birmingham by train so I'm not in a hurry to go back and check but from memory the enclosures were about 40cm long by about 6cm high and had about 10 'cold white' LEDs in each. They are not overhead lights, they are on footbridges and form part of the hand rail on both sides of the bridges. They had frosted diffusers but the points of light inside them were still easy to see.

There are similar 'flashing disco lights" in my village. They are in a pedestrian tunnel under a railway bridge but are larger with an opaque white window. The original lights were fluorescent tubes but they were replaced only a few years ago by LED equivalents in the same holes in the wall. I'm a local community councilor but lighting like that comes under the remit of the County Council highways department so it would be difficult for me to trace who made/supplied them. I can take a photograph if it helps but it's probable the enclosures were specially made to match the size of the old lights they replaced.

Brian.

betwixt said:

Sodium lamps are actually very efficient by the way but being monochromatic causes problems...

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There are several more points I wish to add:

1. Eye is more sensitive to yellow (compared to bluish end) and therefore less light intensity may appear equally bright and acceptable (streetlight use);

2. It has taken a long time for the common high pressure sodium vapour lamp to come on to the street; few years ago we were shouting about the virtues of the CFL (both industry and the government): none of the CFL lived longer than 2-3 years (my home; personal experience) and the problem was with the electronics only.

3. I personally think HPS lamps are still cost effective as a street lighting but newer technologies must be used for new installations.

Thanks, i think another reason we do not see SMPS driven streetlights is that they are expensive, and no-one will take out that expense with streetlights , ..because no-one knows exactly what the mains transient risk is for each streetlight in each location. So realistically, its impossible to design a cost effective transient protector, because you do not know exactly what youre protecting against.....and then there's power system faults to come up against....these virtually cannot be protected against