Precisely, which is why LEDs are not suitable in many cases as direct replacements for GLS/CFL. In other words, change all your fittings to suit our lamps. The 3.5W Aldi LED gets hot in a metal socket in a metal, ventilated shade. LEDs are astoundingly inefficient. Any source of light that generates heat as well should be rated for inefficiency, not efficiency.
Sort of. I was promised a -£5 saving, so in the spirit of negativity I didn't take up the offer and thus saved saving -£5.
I'd be interested to see how you would rate inefficiency of, say, GLS, halogen, CFL, and LED.
At the moment I am struggling to understand how an LED rated at 3.5W could be expected to dissipate more than 3.5W of heat even if it were wrapped up in an aluminium foil overcoat. Certainly that would be zero percent efficient at emitting light, but nonetheless a small overall loss compared against, say a 60W GLS.
No they are fairly efficient probably around 30-50 lumen/watt against the very best LEDs now in production which are now about 80-100 lumen/watt. Research devices have managed much better.
This is dated 2001 and when I did it only green semiconductor LEDs were anything close to competitive. Now high power white LEDs have overtaken metal halide efficacy in production LED bulbs available for retail.
The problem is that whereas the 60W GLS emits some light 12Lm/W and a very great deal of IR and some warm air it can tolerate very high operating temperatures on the glass envelope without any difficulty. You can feel the IR heat radiation in the beam of a spotlight.
The LED consumes 3.5W emits 40Lm/W no short wavelength IR and just increases its temperature until warm air rising or the enclosure can radiate it away. Radiation losses scale as T^4 and don't really become significant until 50C or above so you need free air flow for cooling. The LED bulb is in trouble if its temperature exceeds boiling point.
Put it inside a well insulated luminaire designed to protect timber from insanely hot halogen lamps and you have a recipe for disaster.
A "perfect" optimised monochromatic lamp would give about 700Lm/W. If it has to be white then as a black body 100Lm/W is the limit but if you can cheat and only emit visible light then 250Lm/W is the target to aim for. For a very long time the most efficient lamp was a large ~100W low pressure sodium street lamp at 200Lm/W.
But the white LED technology is still improving all the time and Cree have claimed one in the lab at close to 100% thermodynamic efficiency:
Depending on what you set as the target for maximum white light efficiency the incandescent is 5-10% efficient and the latest consumer LEDs 20-35% efficient at turning electricity into white light. That still means the majority of power used is turned into waste heat.
Things are much worse if it has a nice shiny metallic surface finish on the heatsink as that prevents thermal radiation getting away.
Quite. Which is why I questioned the statement "LEDs are astoundingly inefficient".
moubt of time. If you leave LEDS on for that long their life shortens quite quickily.
ast much longer than ordinary bulbs, this equates to about 25 years if used for a few hours per day."
life if they were on 6-8 hours per day.
and non were meant for mains lighting.
Those weren't meant for dometsic home use were they. So little point in com paring them with todays range.
what does that demo ? Last week I ordered 4,000+ LEDs .
yes, now we have 'shades' and tempratures of WHITE they weren't availble in the mids 70s more like the mid 90s.
So why say if run for a few hours a day6, have you ever seen such a standme nt of CFL or tungsten.
No they aren't, it's a marketing ply to the stupid they can buy a bulb for £10 that'll last them 25 years and save them money........
Which doesn't equate to home use.
If they really did last anywhere near the quoted life span then they'd be w illing to guarantee them, but so far they haven't why ?
Exactly.
% failed in under a month, mosty likely fakes.
OK then you can be the test then.
hours a day ?
IT IS THERE READ IT.
I did for work we want to test them too. LED tubes.
I have a light meter at the ready, but unfortunalty the college blinds don;t keep out much light which makes it difficult to compare them with the 'normal' at this time of year the ones we get supplied for NOTHING. If I am to replace them all I need 84 for the labs and 16 for the offices. I can't just spend nearly £5K just because they last longer providing we don't use them as much.
I have little use for LEDs as lighting in the home. from my experince they do NOT give the same quality of light either, I do n ot see them as more efficient yet, unless willing to pay a lot more for the lastest models.
TUBES not bulbs brought them in April for work NOT the home.
anyway I think the future is with PLEDs for lighting and OLEDs for gadgets.
The plastic(?) part is just hot to touch, i.e. a bit more than warm, so I'd assume up in the 50s given the poor conductivity of the surface. The metal shade is just warm around the base of the lamp (~24C in here atm).
I tried it with a Maplin plug-in meter, expecting a poor PF: it was, at about 0.6, but the readings were 2W and 3VA. I suspect that the meter doesn't like the circuitry.
This fitting is a somewhat shiny filing-cabinet grey, so not extreme.
Useful information, thanks. I'm very interested in LEDs (started using them back in the '80s at work for indicating lights on machinery etc.) but also rather disappointed in how far they haven't come in 30 years.
Anything that isn't shiny metallic is a pretty good "black" in the thermal IR band (except possibly for some specialised military paints).
They have come a long way in that time. The early ones could only handle about 10mA if that and were dim as anything. Modern ones are brighter by more than an order of magnitude at the same current.
One handy trick if you live somewhere prone to power cuts is to bridge the switch on an LED torch with a 470k resistor. This makes the LED glow just enough to find the torch in total darkness without losing any noticeable battery life. You can see by it when fully dark adapted.
The 14(*) distribution regions charge differing amounts to the suppliers to distribute the power from the National Grid to the end user.
They are ball park and as I can give them fairly accurate usage information not bad, ie within a fiver. I use the comparison sites as a filter to find the cheapest half dozen or so tariffs. I then get the real figures for those tariffs and plug them into my spreadsheet. The last time I swapped suppliers the total monthly payments dropped from £295 to £187.
(*) 14 regions but only 9 actual companies, though I should imagine each region "owned" by the same DNO is operated as completely separate entities.
Are they a straight swap or do you need to change the control gear in the fitting as well?
Oh, I accept that. It's just the fact that they still waste energy as heat and can't give omnidirectional light.
Interesting tip, thanks. I have several torches around the place (the cylindrical ones from pound shops, rubber push-button on the end, are v. good for the price) and I seem to locate items accurately in darkness (no SWMBO to 'tidy up') but in a situation of necessity the glow would be good. The desk lamp mentioned up thread has a switch that glows green - saves having to turn on a light...
Next question: Why do the distribution regions charge different amounts? ;-)
I'd guess that it's historical. The regions match the old electricity boards, who had different tariffs as they were distinct entities; presumably they had different costs to justify that.
I've no doubt that providers just use the regions as a means of maintaining profits, I can't imagine that there is any realistic cost basis for the variations any longer.
According to the information supplied they should fit and work.
I also read up that there could be problems with rotating machinery and that sometimes the reflectors need changing although I've yet to work out how a reflector would stop flickering but perhaps it's a reflector diffuser type coating.
Differing costs in distribution. You have less cost per customer served in an urban area compared to a rural one. Take the average residential street with the 10 yd frontage, 170 odd customers per mile. Around here they are lucky to get 2 or 3 customers per mile. Some regions are predominantly rural others have the huge conurbations and little rural.
Interesting theory but I don't think the stats bear it out. For example Northern Scotland has slightly cheaper prices than London.
What about dividents for shareholders and other perks for managers and employees, surely such things are similar to supermarkets why should a loaf of bread be cheaper in one shop than another if they are next door ?
Didn't early light bulbs have a fairly hard vacuum "filling". Modern bulbs are gas filled, AIUI the gas filling enables better cooling of the filament but shortens the life, maybe by enabling the filament to be much finer and run hotter.
Yep; the Chinese 7W (7x1W) PAR30s I bought months ago haven't failed yet and, to make sure of that, I left them on around the clock for days on end - reasoning that early failure would be weeded out that way. Their normal duty is many hours per day anyway - at least, until the start of summer. They still survive, and I reckon on buying more from the same seller on ebay -
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