A chance discussion with a couple of work colleagues today has made me curious about LED lighting.
Has anyone tried it and in a position to offer some opinions, please?
We've got CFLs in most places, small incandescents in some wall lights (which need dimmers), and some halogens. For a "work light" over my desk or work bench I favour a halogen. CFLs I can "tolerate" but I'd not like to go any "dimmer", I'm not convinced by the supposed "equivalence" statements on the CFL packets!
How have people found LED lighting in say, desk lamps, bed side / table lamps, wall lights, central lights, please?
It is as well to move up one step for true equivalence. Otherwise you get marketing men as opposed to engineers equivalence ratings.
The thermal design has to be absolutely spot on if the high intensity high power LEDs are not to cook themselves with consequent loss of output due to thermal and photo degradation of the encapsulation. The typical core device is rather like a point source which gives harsh shadows although practical consumer designs have several in one package.
Treat all claims of MTBF with a small pinch of salt, but the major source of trouble is thermal - they don't radiate away enough short wave IR like a hot filament does so all the waste heat they produce ends up as higher temperature. The emitter runs quite warm and will fail prematurely if the heatsinking is inadequate.
They are pretty good as self collimated spotlights which is something where CFLs are worse than useless. They are very effective in roadsigns which can be designed to be visible at long distance without being too dazzling at close proximity.
Do you know what I mean by "filmic effect" on a DVD? Where everything seems to be in sort of stop-motion? It was weird to see it in real life as I poured coffee out.
I've got one in a long hall to give some instant light where the CLF's don't come on immediately. Must have had it a couple of years now and it does just what I wanted.
I bought two candle ones recently for the hob extractor light. The filament ones failed very frequently so I reckoned that it was worth trying LED ones - much brighter and have made a noticeable difference to the hob lighting.
The other LED light I have is the goose-necked spotlight for my wood turning lathe. I mention this as one of the things I hand't thought about with these is that the stroboscopic effect is pretty noticeable.
I'm afraid Martin Brown's waffle about short wave IR is in suitably scientific jargon to be believable. Heat is heat and in the context of an incandescent bulb exists because the filament is white hot - because a LED is effectively current driven it generates a greater proportion of heat than would be expected for the low voltage across it. Good heatsink design.is required for that and is probably the difference between quality LED lamps and those that die early.
They are now suitable for some uses in the home, and those are growing as they improve. Low power spotlamps would be the most effective at the moment.
Commercially, they are coming on in leaps and bounds, but prices are well outside of domestic use. I was at a trade show last week and there were lots of impressive products on show, but you need to be sitting down if you ask for any pricing. However, there's very little targetted at existing lighting, because LEDs make lousy retrofits for CFLs or incandescent - I only saw one which claimed to be a 60W GLS retrofit (and in the situation it was in, I couldn't judge how well it really matched 60W equivalence). Whole fitting replacements for MR16/GU10/R63s exist from several manufacturers, which means these are probably going to start becoming affordable on a domestic price scale first, but not there yet (although a friend has just done his kitchen ceiling with them). I was also pleased to see many component suppliers (LED parts, heat sinks, drivers, optics, etc), as I tend to make my own.
There's a new part-solution to thermal problems for high power white LEDs, and that's to separate the phosphor from the LED, so the heat generated in the phosphor (due to Stoke's shift) is generated away from the LED chip which is the heat sensitive component (although it still generates plenty of heat itself, so this isn't a complete solution). I did wonder about the safety though, as the intense blue LED naked sources often used to generate white light are very harmful to eyes (can cause delayed blindness in 24-48 hours).
One company was demonstrating a dimming LED which did the same colour shift as an incandescent when dimmed, which ran on a conventional phase dimmer. I had played with doing this some years ago, and I must say, it was a very pleasing effect. It's not a product yet. They currently sell LED lights with variable colour temperature under program control.
So in summary, I think we'll see some significant developments in domestic lighting in the not too distant future, but we're not quite there yet.
I'm afraid Rob Graham's waffle about the proportion of heat generated by the LED because it is current driven may be suitably scientific-sounding to be believable but power is power and the amount consumed by an LED lamp or anything else is the voltage drop across it multiplied by the current passing through it[1], regardless of whether it's current- or voltage-driven[2]!
[1] for DC [2] i.e. driven from a source that tends to maintain a constant current through, or a constant voltage across the device.
Yes, was quite pleased with MR16 LED equivalent of 20W halogen (CPC LP0439987 £4.37 ea) fitted in a desk lamp.
Last time I was in Clevedon I noticed they had clear festoon lights along the sea front promenade which turned out to be LEDs with what looked like clusters of standard 1/4"-ish white LEDs visible inside the golf-ball size glass (polycarb?) housings. They must have been equivalent to 20 or
40W incandescents I guess, so an impressive power saving overall. I did notice that a few were out so presumably reliability still leaving something to be desired.
I've had 60 individual LEDs running continuously for a couple of years off a 12 volt car battery. Half of them have failed, probably because the battery was being charged. Make sure the voltage is not too high.
I'm putting my money on GU10 fittings. Can use incandescet now, but this seems to be a fitting of choice for mains powered LEDs so I'm hoping to be able to start using in earnest in a few years as they improve.
You should never put them on a voltage source without a limiting resistor in series or better still a constant current driver. You can just about get away with it using a pair of spent AAs and a red LED in a torch for astronomy but it isn't to be recommended.
Christmas LED lights designed properly should last until the cables deteriorate due to weather or wire fractures from bad handling. There are still original LED indicators from the 1980's operating in old gear.
A filament lamp has a nice voltage current curve to protect itself - filament resistance increases as it gets hotter. LEDs have no such inbuilt self protection and current through them increases very rapidly for tiny increases of voltage above the point where they light up.
It isn't through being current driven it is because it emits light with a higher proportion of visible and almost no near infrared. It has to rely on conduction, convention and thermal band IR for cooling.
The difference is that any waste heat the LED produces goes entirely into heating up the plastic and phosphor around the die. Without a decent heat sink high power LEDs last just a few seconds.
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comparison most of the power dissipated by a 3000K filament bulb comes out with a peak wavelength of 1um and radiative heat losses to the environment are much more important. You can feel its effect under a kitchen spotlight beam only about 10% is as visible light.
It is a double irony that retrofitted to traffic lights LEDs sometimes don't produce enough waste heat to keep the enclosure snow free in winter.
GU10 retrofit LEDs will probably get a little better, but will always be a poor compromise (unless someone discovers a new LED technology which can run much hotter - something that has eluded the industry for decades so far).
What you'll see are LED lights which replace the whole GU10 fitting, where the LED element is not separately replaceable. These exist now, but will expand in popularity as prices drop, and will well out-perform anything a retrofit GU10 could do.
I have experiments with LED lighting for a number of years using eBay suppliers.Lots of screw type white LEDS around.
The best I have found for practical use and elegance are the LED strip lights. These provide approx 300 LEDs in a 5 metre roll and can be trimmed to length, powered by small 12V mains transformer.
I use the warm white as a strip under the hand rail up my staircase. The LEDs cannot be seen directly and just a warm white glow from the rail so attractive.
These LEDs wire up the darkest part of my house, use approx 12W, and I keep them on 24 hours now. They are a rather beautiful (in my opinion) light feature of the house, and very useful for safety of staircases, I ended up in A&E after a recent fall on the stairs. The magnolia painted wall reflects light bright enough to illuminate bedrooms also. The effect of permanent lighting on my staircase in these early evening lights adds cheerfulness to my otherwise dark and sometimes quiet house.
LED strips means I don't use my hall or landing fluorescents (which take 1 min to warm up and seem to fail quite regularly) so that saves
3 bulbs.
I have a strip under the kitchen wall cupboards but made the error of using white not warm white, which gives a cold effect.
I also use Red Green Blue LED strips in the lounge under a book case. These have a remote control mixer so allow many colours and sequencing effects. Just trying them in my bedroom also fixed on top of window frame, behind white curtains to soften the room light.
All kits are less than =A320 inc transformer.
There are waterproof variants so I might fix some up in my garden.
Christmas lights have come early to my house but will be a permanent fixture!
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