LED domestic lighting

driving them like this also means you can pump more current through them thus making them brighter (maybe this is the reason rather than saving battery life?)

Reply to
Dave
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Sorry, but this is a very common misconception. They can produce excellent high brightness narrow beams of light, which a filament lamp can't. This can be an advantage in some applications like spotlamps so the beam might look brighter than a filament lamp. However, if you take something like a 10º beam angle, which is 78 square degrees, and divide by the 41253 square degrees in the sphere which a filament lamp lights, this shows that the LED is only lighting up 0.2% of the area which the filament lamp did. That's why they appear so efficient, but in fact they aren't.

Nobody can currently get 30 lumens/watt from a white LED, which is what you get from highest efficiency halogen lamp. Nichia are predicting 60 lumens/watt for a product they expect to ship in

2005, which is still less than a fluorescent lamp. The efficiency improvement manufacturers have managed over the last couple of years is very disappointing compared with what went before, so it may be that some type of limit has now been reached without a significant change in technology.
Reply to
Andrew Gabriel

The mean brightness is still the same, since the mean current must be the same, because you can't leave the LED on at the current used when on or it will burn out. However driving them switch mode allows the circuit to run more efficiently which IS why they are pulsed.

Steve

Reply to
Steve

Mary: I agree. I don't think I can even speleologically spell that anyway! Terry.

Reply to
Terry

In message , snipped-for-privacy@isbd.co.uk writes

You can certainly buy cycle lamps with what are described as halogen bulbs - btw, has the law been updated yet to allow cyclists to use non-filament bulbs?

Reply to
ignored

"Dave Plowman" wrote | Mike Barnes wrote: | > Well, yes, but they'd only need to be replaced every few decades. The | > lamps, that is. | I'm not so sure. Once you start driving LEDs hard as a light source rather | than just an indicator, their life span reduces dramatically.

I noticed last time I was passing through Waverley that the solari-style LEDboards had some characters missing.

The main concourse ones were advertising trains calling at Newcas and Leices and the ticket hall ones were welcoming passengers to the First ass Lounge.

Owain

Reply to
Owain

"Steve" wrote | >>My curiosity knows no bounds, it appears. When I bought one of | >>those LED cycle lights, I hooked up a sillyscope to it and | >>discovered that on the "steady" setting, it actually spent 3/4 of | >>the time switched off. 100 Hz square wave mark to space 1:3. | The mean brightness is still the same, since the mean current must be | the same, because you can't leave the LED on at the current used when on | or it will burn out. However driving them switch mode allows the circuit | to run more efficiently which IS why they are pulsed.

Is there a certain frequency above which this pulsed light is considered a continuous light and therefore acceptable as the continuous light required under the Road Traffic Act or whatever legislation says that flashing lights on bicycles are verboten?

Owain

Reply to
Owain

Well LED rear lights have had BS markings for a while and now the new LED front ones do as well so presumably they're legal as they conform to the required British Standard.

Reply to
usenet

They're common as centre stop lights on cars. And as all the various tail lights and indicators on buses. Oh - and the taillights on my BMW. And of course there are HID headlamps (xenon) which aren't filament lamps either.

Reply to
Dave Plowman

Actually LEDs get slightly more efficient at higher current, so the mean brightness is higher.

Furthermore, it appears that eyes don't perceive mean brightness, but perceive something which is between the mean and peak brightness, so a flashing light will appear brighter than a steady light of the same mean brightness (over some frequency range).

Neither of these effects is very large though. I've seen conflicting reports of which of these effects first resulted in pulsed operation of visible LEDs, although the high pulse current techneque was used to drive infra-red LEDs before visible LEDs were invented.

Reply to
Andrew Gabriel

The police are probably just happy that a bike actually has lights

Reply to
geoff

That certainly used to be true, but again for the Luxeon jobbies we use, it ain't anymore.

Is this a medical fact ? In recent discussion on sci.elect.design, this effect was poo-poohed by several of the engineers in there whose opinions I would trust.

Steve

Reply to
Steve

I've seen it stated on a number of occasions. I have not personally tested it but it sounded plausable. BTW, the frequency range over which it works is not wide. It needs to be above the optical fusion frequency (varies from one person to another, but never higher than

70Hz), and below the frequency response of the receptors and optic nerve (which I believe is always over 100Hz, well over in some people). One person I spoke to about it a while back didn't think the frequency response of the optic nerve was the upper limit for the effect to work (thought it was higher). These frequences vary a little across the field of vision too, and with other factors.
Reply to
Andrew Gabriel

Early LEDs did have a light output that increased more than the current increase, so it certainly made sense to operate LEDs in a high current, low duty cycle pulsed mode. Modern LEDs are more linear, so the only reason for pulsing would be to make the brightness adjustable (or constant, as the battery goes down), or maybe to resolve differences between the dc supply and the LED's fwd voltage drop (but that would need an associated inductor/transformer).

I have also seen the opinion on another newsgroup (c/w research references) that pulsed LEDs can appear brighter in conditions of low ambient light levels (ie, if our eyes are dark-adapted).

Reply to
Tony Williams

The only restrictions relate to steady lights and red to rear.

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I believe some flashing lights are now allowed, but can't find that.

Reply to
Nick Finnigan

Is the Act enforced?

Mary

Reply to
Mary Fisher

But they're not pedal cycles ...

I have my own Toy Boy, thank you :-)

Mary

Reply to
Mary Fisher

I'm really glad I asked this question.

I think.

Mary

Reply to
Mary Fisher

It's T H A T, Terry ...

Mary

Reply to
Mary Fisher

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has a PDF about a forthcoming 3200k" Warm White, Incandescent-Equivalent LED" shipping in August (it talks about LEDs "rapidly gaining traction" in general lighting, ...we give them a byootiful language and what do they do to it.............)

3200K is around quartz halogen colour temp (tho being flouro based I'm guessing the "quality" of the light whould be like that of a Warm White fluro) IIRK one of the probs with white LEDs is the colour isn't stable with time.

Lumileds has some impressive 5w suckers with heatsinks on the back but it's Nichia's 50mW blue or violet lasers that I covet!

Reply to
Duckweep

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