Reported in the Lancashire Evening Post tonight - the County Council want to replace the county's 145,000 street lights with "computerised 23W LED bulbs" that can be controlled wirelessly.
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the group's penchant (sp?) for discussing lighting, have LEDs reached the stage where they can be considered bright enough to be used for street lighting? The 36 (IIRC) LED spotlight that I got for a part of my pond is utterly bleedin' useless so I'm sure it'll be a field-day for all the local pikey types if they go ahead with this half-baked idea.
Pete (who should be testing his shower but the battery in my meter has gone and local shop hasn't got any - typical eh? :o))
LED technology has improved beyond belief in the last couple of years - and even in the last few months. On my last visit to Vegas back in October 2008, I took in the new Kris Angel show. It was crap, but some of the sets made use of LEDs, notably one where a pair of odd machines that were a sort of a cross between a TV studio camera crane, and a JCB digger, 'fought' one another. At the end of the arm on each, was a rectangular panel of perhaps
40 high power LEDs, and when they swept across the audience, they were blinding, to the point where they hurt your eyes, and I was sitting perhaps
100 feet from the stage. Almost all of the architectural and decorative lighting in Vegas is now LED based. There are many many LED based 'giant' TV screens along the Strip, and these are also so bright that they are fully high-contrast visible in midday sunshine, and at night time, are bright enough to hurt your eyes.
I recently installed some single white LEDs in reflector mounts into kickboards that I made for my new kitchen (after the missus saw similar in a display kitchen in Wickes, and I nearly fainted at the price). I ordered a variety of high intensity white LEDs from Farnell, and then experimented with how they looked at full chat, and dimmed to varying degrees. Running them in series strings at about 20mA results in a power dissipation of around 60mW each, so just under 1 watt total for the 15 of them. During the day, they are intensely bright. At night, they light the kitchen to the point where you would be able to find anything you needed in a cupboard - and remember that these are just 2 inches above the floor. One such LED that I had left over, got grafted into the end of an old biro pen, and hooked to a block of rechargeable batteries. It makes a really useful 'torch' for looking into places where you can't get the bench light to shine in, like DVD mechanisms and such. This LED is so bright at just 10mA, I think that it would actually be possible to damage your eye if you looked directly at it for long enough.
Although I don't think that LED lights have quite reached tugstens / halogens yet in terms of eveness of illumination, eveness of spectrum, and colour rendering, I think that they are now getting very close, and are at least as good as CFLs now - not that I think that CFLs are 'good' in any of these respects. Judging by what I've seen of them, I would say that they are easily good enough for street lighting applications already. I expect LED lighting in the home environment to overtake CFLs now in fairly short order. If anyone is interested in following this technology's development, go to Rapid Electronics' website, and sign up for their weekly newsletter. There is stuff about the developmental work on LEDs and LED lighting in just about every issue.
149-7969 set in 232-312 deep-recess holders. I used a flat-ended router bit set in a bench press to 'drill' a hole to the depth of the holder's rim, and then a regular drill to go the rest of the way through, resulting in a sort of 'stepped' hole if you like. The hole for the rim was a tight push fit on the holder, so no retaining nuts etc required. Holder just pushed in (after painting and laquering of the boards of course) until it sat flush with the surface. This gave the best looking lighting effect. The 15 LEDs that I used were divided in three series strings of 5 LEDs each, so requiring around 20 volts or so per string. I fed them with a simple adjustable constant current source, built around a bog-standard LM317 adjustable voltage regulator. (1 x LM317, 1 x fixed R, 1 x pot.) Once the holders are in place, the LEDs are fitted from the back, retained by a little plastic screw-in cap, with holes in it for the leads.
The effect from these lights is very pretty - particularly at night when they cast a sort of 'scallop' pattern of light across the floor. They are
Your experience is most encouraging. I am sure you are right that LEDs are going to be one major source of lighting soon. I bought some high output LEDs a few years ago intending to build some panels for emergency lighting. I found that the LEDs varied in brightness quite a bit. I suppose it didn't really matter, but I found the effect unacceptable. Is the consistency of the ones you used good, or did you have to select them experimentally so they matched? I've got a 30 LED rechargeable inspection lamp which is very bright. It is also directional which saves the glare in the eyes in dark spaces. And you don't trip over the cable!
I bought the LED GU10 replacements from B&Q for my gangway. They shone slightly more than nightlights and had a strong blue tint. They went back. For GU10, halogen it is for me just now.
I used them as they came out of the packet, Peter. No cherry-picking at all. As they are arranged in series-connected strings of five, the current through each one is of course identical to the other four. I have arranged it such that the current through each string is also identical, so the overall effect of the connection strategy is that every one of the 15 LEDs has an identical current passing through it. From a light output perspective, there is no perceptible difference between any of them, so I would say that the electrical and emissive characteristics are close enough as they come out of the factory, to not require any further 'select on test' regime.
Presumably you added a series resistor to pad the current to a standard value in each string? Perhaps I'll look again at my emergency lighting project and try to find my stock of resistors. Where do the little buggers get to? Oh yes I've got to find the LEDs as well!!!
No. No series resistor (as such). One is not needed if you feed a string - or indeed a single LED - from a constant current rather than constant voltage source. Constant current or limited current pulse drive, are the preferred methods for driving modern LEDs that are not being used as simple front panel indicators. A simple constant current source is easily and cheaply constructed by clever use of a variable voltage regulator type LM317. All that is needed is this three pin device and two resistors, one of which is a variable if you want to be able to dim your LEDs. A single resistor if you don't need them to be adjustable. The formula for calculation of your resistor values to set the current you require (typically 10 to 20mA for 5mm LEDs) is a very simple piece of maths. If the LEDs you have are old, start again. They have become much more efficient in the last year, and new ones, ever improving, are coming out from the main manufacturers, almost weekly.
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at this link. If you Google "LM317 constant current source" you will get loads of hits ...
a small (0.9"x0.6"x0.6")module converting 85-265V AC input to 3W/700mA constant current output, for either a single 3W LED or a number of smaller ones. For about £2.50 *including* shipping from Hong Kong...
These modules are what you find in the lower cost 3W big LED GU10 type lamps, remember it will output 700mA whatever the load, even if its a
20mA 5mm LED......
Realised my above link might have broken , it is to Mouser, who now have catalogue pricing availible in GBP, Supertex CL2 , 5-90V in 20mA out in 3 pin TO92, 30 odd pence plus the VAT.
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