I had a pretty good idea that LEDs would be developed faster than the 5 years the experts said not long ago.
Prohibitively expensive and will want to see the test results for light output and colour but they are getting closer. With any luck our supply of incandescent bulbs will hold out until LEDs become practical.
At last. Some sanity. IF they last.
Now I wouldn't mind all LED lighting
understand why they cannot make a bulb with a number of LEDs which operate on different wavelengths to give a more balanced colour. I have tried to achieve the same with a light holder for three bulbs in which each one has a slightly different white light. i think it is an improvement.
Jonathan
Cree have an `Easywhite' range which integrates several dies into one unit; is that what you mean?
dan.
"Jonathan" wrote in message news: snipped-for-privacy@d26g2000prn.googlegroups.com...
I've often thought that too. Also, why not bond the individual LEDs to a sort of 'spherical' heatsink that allows light to come from all directions like you get from a conventional filament? If that happened over just a hemisphere, it would be an improvement. I was interested to read that the guy reviewing in the article stated that there was no reduction in the light output over the lifetime of the lamp. Unless there has been a significant improvement in the technology in this regard - and I don't for one minute dispute that *might* be the case as this technology is developing fast - the light output of LEDs is not fixed for life. Depending on how they are driven, their light output can be expected to fall by up to 50% as they age. As I understand it, this happens sooner with DC drive rather than pulse drive. I'm guessing that these bulbs are probably pulse driven, as that's the best way to achieve a maximum light output from any given LED. The downside is that slightly more complex ancillary electronics are needed, although there are now chips that provide a fully integrated solution with next to no external components, and which hang directly across the mains. All in all, a better overall solution in my opinion than CFLs, but still with a long way to go to seriously rival incandescent lighting for sheer simplicity of manufacturing and the energy budget required for all aspects of that and their distribution, end-user cost, and end of life disposal costs and energy budgets.
Arfa
Though it flickers; some of us find that rather unpleasant. I have two LED downlighters in my porch, and that is all I'd use them for. I put the bulbs in the lounge light (a 3-spot GU10 thingy) briefly and it was horrid.
Neil
That's just the frequency in your particular units, though. I can't see any reason why pulsing at (say) 1KHz wouldn't solve that (or 10KHz or 100KHz). I don't know the LED technology in question, but LEDs in general can cope with those sorts of frequencies.
Theo
Agreed. I'm surprised that Neil could see the pulsing, as this is usually carried out at a fairly high kHz rate to get the efficiency of the drive electronics up. Possibly, what was being seen was some residual mains frequency ripple, for some reason ??
Arfa
You might get beating effects when near the frequency of (say) the 15.625KHz line rate of a CRT TV, or being a close-but-not-quite multiple of the 100Hz flicker of a fluorescent tube. But this sounds unlikely.
Theo
I don't think LEDs cope with high frequencies at all. I remember experiments at university many years ago, building an LED beam communication device, and found that the light output dropped rapidly with frequency.
I've done pulse-width modulation at around 10kHz with no apparent ill effects (though without the benefit of scientific measuring devices).
This was on medium-power (1W or so) RGB leds.
I don't know about LED lighting, but I do know that when driving at night through some local junctions with pedestrian crossings, the flicker of the red man is extremely distracting in my peripheral vision.
SteveW
Don't know, but I can see flicker on pretty much all the ones used on premium cars as well. It can be a bit distracting while driving in the dark.
I know I'm fairly sensitive to flicker, as I can't use a traditional CRT monitor on a refresh rate of less than about 75Hz without feeling seriously yucky after a very short period of time.
Neil
I'm not sure what that is caused by, but the 'dotted' persistence trail that it leaves in your vision at night when you flick your eyes to the side, annoys me as well. The missus claims she can't see it ... It could be because the LEDs in the stop / tail light clusters are multiplexed into blocks, and driven at a fairly low rate, or that the same LEDs are being pulse width modulated to 50% at a low rate for 'tail' function and then upped to 100% for 'stop' function. I sort of suspect that it is the latter, because when the drivers of these cars brake, the flicker goes away. Of course, it could be a combination of the two techniques.
The orange lights on top of traffic cones do it as well. That is almost certainly because they are driven with big, but very narrow pulses, and at a low rate, in order to minimise battery drain whilst maximising light output. Just as an aside whilst we're on those cone-top lights, can they communicate with each other in some way ? I've noticed more and more that when the use them over a couple of hundred yards to shut a lane down, although there is no physical connections between them, they definitely work in 'timed harmony' to produce a 'travelling line' in the direction you are going. I thought at first that it might just be coincidence, and I was seeing them being approximately in sync with one another, but the more I see it being done, the more it looks like that's not the case.
Arfa
This paper suggests that traffic light LEDs can be modulated at 100KHz:
Theo
YMYA
Arfa
Thank you for making me look it up. I'd wondered about them, too.
That's exactly what some manufacturers are doing.
MBQ
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