Nice topic, now you got me started
IMHO for standard lighting LEDs are not yet a good choice.
For torches/flashlights however they are perfect. I see absolutely no reason for incandescant lights here any more.
I've been a LED-flashaholic since the first white 5mm LEDs from Nichia appeared, in the beginning modding incandescant flashlights with self-made step-up circuits (the famous LT1932 started it all). In the meantime I try to keep up with new products, but now have reached a stage where all my friends and relatives already have LED flashlights so I have nowbody to give/sell them
. As a consequence I have to stop buying new lights now...
All high-output LED applications suffer one problem: HEATSINKING.
LED chips must be kept cool, else they have low effiacy (lm/W) and degrade very fast (only a few thousand hours instead of 30 or 50'000).
This is the MAIN problem when trying to replace existing light bulbs with LEDs: a good 15W LED can replace a 100W incandescant bulb lumen-wise, but needs a heatsink theat is MUCH bigger than the original 100W bulb. So forget incandescant replacements with more than 5W LED power.
Good LED-based light fixtures have to be designed 'from scratch' with LED heatsinking in mind!
Lifespan: yes, 30 or 50'000 hours are possible (IF the manufacturer has his processes under perfect control, which may of them DON'T), but only with perfect heatsinking. All LED replacements for standard bulbs I have seen so for DO have thermal problems and will never reach the promised lifetime (like many 'energy saving bulbs' too, BTW).
Car headlights:
This is an application where LEDs can now just be used. They are about as efficient (lm/W) as HID (Xenon), but they don't require high voltage.
The optics are more difficult than HID because you need a multi-emitter light with separate lenses for each LED - the existing 20W or 30W single-emitter LEDs are too large and thus impossible to focus (the optics designer wants an emmissive area as small as possible [no more than 2x2mm²], else the lenses become too large).
BTW: the R8 headlights have an active cooling system: a fan. The warm air is directed to the front glass to prevent icing in winter - mind you, LEDs don't emit any IR radiation, so the headlights would soon be covered with ice and snow - just one of the many side-effects to be concerned. Also considered in the design stage: what happens if you park your car in direct sunlight, heating the front lights up to maybe 80°C, and then switch the lights on (e.g. in a tunnel)? LED chip overtemperature! Solution: temperature measurement, active cooling, and: dim the lights.
For home lighting: see notes on heatsinking above.
In my home I have flourescent tube lighting with electronic ballasts (no "energy saving bulbs") everywhere. Efficiacy is 80-100lm/W *including ballast*. Lifespan is 20'000 hrs (20 years at 3hrs per day!). Cost of one 36W tube with 3200lm output: 5€ - that's about what you have to pay for 300lm (1/10th) of LED light (only the chip)! AND, most important: the quality of light (colour rendering) is BETTER than with current high effiency LEDs. Yes, there ARE high-CRI (Color Rendering Index) LEDs, but at the price of lower efficiacy (50-60lm/W instead of 100).
Conclusion: I see absolutely no reason to replace my home lighting with LEDs in the next 10 years. Flourescent tubes are 10 times cheaper, more efficient, last just as long, and they have better colour rendering than current LEDs. But I'm thinking about HID in 2 places where I want more directed light (spots) than tubes can deliver.
Ok, I like BRIGHT light at home. If you like it DIM, LEDs may already be ok for you
Please don't believe I'm an "LED-hater" - the contrary is true! I've been watching the market for many years. I have many LED flashlights (mostly Cree LEDs). At work I'm involved in designing the electronics + software for meanwhile the 4th LED surgery lamp (160'000 Lux @ 1m, 2700lm OTF [that is >4000lm LED output] 4200K, CRI 92).
For many applictions LEDs are great, but I just can't see the advantages in general lighting (yet).
Currently, the lighting companies are trying to sell sometimes pure rubbish to consumers. If they go on like this, the will ruin the LEDs reputation just like the first "energy saving bulbs" did with their horrible light. I can't stand all the bullshit written about LEDs in internet stores, on ebay, in forums, etc.
Wait another 10 years until there are established standards for LED 'bulbs' and fixtures.
09 Jul 2010, 13:49
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