LEDs are mature

After purchasing some LED flashlights locally, I was a skeptic about LEDs. Recently purchased an LED headlamp that uses a Cree XM-L2 T6 LED. It blows away my DeWalt 14.4 V flashlight. Lights up the whole backyard. The casting of light is very smooth too, no filament distortion. The thing is powered by one 18650 3.7 V lithium-ion battery, supposed to last for over three hours on blinding light high. Pretty amazing IMO.

Reply to
John Doe
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I have a couple of street-light grade LEDs. At 12 volts/1 amp, they look like welding arcs. Blinding.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

If you need a tiny spot of light, they are blinding. But, for area lighting, pulling the round number 100 lumens/watt out of my ass, you've got 1200 lumens. 100W incandescent can do better than that.

Reply to
mike

If you need a tiny spot of light, they are blinding. But, for area lighting, pulling the round number 100 lumens/watt out of my ass, you've got 1200 lumens. 100W incandescent can do better than that.

Most modern high power LEDs can now easily achieve 125-140Lm/W. The mid power chips we use are rapidly approaching 200Lm/W! Incandescent is still well

Reply to
JB

Some of them the active LED die is now approaching the luminosity of the solar photosphere when running flat out on a decent heatsink. It tends to degrade the phosphor and darken the plastic at that intensity.

You must live on a different planet then! The melting point of tungsten limits incandescent lamps to typically no more than 20Lm/W round here (and 15 is a good working number).

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A few projection bulbs do better Lm/W with forced air ventilation and short working lifetimes but incandescents are much less efficient.

LED efficacy at converting electricity into light is fast catching up the ultimate monochromatic low pressure sodium lamp in terms of Lm/W.

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Regards, 
Martin Brown
Reply to
Martin Brown

It is not completely fair to compare 100W to hot wire and 12W to LED.

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-TV
Reply to
Tauno Voipio

I think the point was that a 'street-light grade LED' at 12W would give about 1200 lumens, which is comparable to a 100W incandescent, and might seem a bit low for street lighting.

The lamps I took from street lights as a kid were 150W, so in fact 1200 lumens of LED would be in the right ball park, particularly with the better control over the lit area.

Cheers

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Syd
Reply to
Syd Rumpo

Reply to
upsidedown

It's also not a tiny spot of light. It's more like a car headlamp, if not brighter.

Reply to
John Doe

Running a LED well below rated current, it is possible to achieve

50,000 - 100,000 hr life time with acceptable luminance degradation. Assuming 4000 hr/year street lighting this is about the expected life time for poles and fixtures (20-30 years), thus, there should not be a need to replace the lamp during the pole lifetime.

For such life expectance, the LED needs to be run below 1/3 of the rated current. In fact, the life expectance of the control electronics (especially electrolytic capacitors) may be the limiting factor.

Currently discharge lamps have to be relamped every few years due to light output degration. Avoiding this would compensate the cost for larger number of LEDs in the fixture.

Reply to
upsidedown

Sounds like it's finally possible to use them as a strobe, though a flash tube is still probably cheaper.

Reply to
Tom Del Rosso

The claims from reputable LED manufacturers (eg. Philips) are more like 2-3x the life of the most popular discharge technology (Sodium)-

60,000 hrs vs. 20-30,000 hours. Of course inadequate cooling etc. can reduce that..
Reply to
Spehro Pefhany

Minimum duration of flash for a given total light output may be disappointing if you don't grossly exceed the specs.

Reply to
Spehro Pefhany

We've used them for human vision strobes.. 10-100 ms on times (not sure of the exact number.) But not for stop action photography.

George H.

Reply to
George Herold

Yup. Overcurrent causes migration of defects and interstitial atoms--you can see it in the 1/f noise. The die basically disassembles itself. High temperature aggravates that.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

My billboard LED drivers (25mA) are spec'd at 25ns max TR/TF. I don't know about light output, but I've had a recent inquiry to quote using my (patent-pending :-) scheme for cellphone camera flash. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Not my design, but the issue was not on/off speed (in this application) but getting enough photons into the eye. (used to measure the angular frequency of a pool ball rotating in a spherical air bearing.) In room lights.

George H.

Reply to
George Herold

You're missing my point. It's not about efficiency. I merely used some random efficiency numbers as a back door approach to guesstimate how much light might be coming out of the LED. I compared that to a 100W incandescent and suggested that the LED in question ain't "blinding" when used as area lighting.

Reply to
mike

I got a nice LED flashlight for Christmas. I looked at the LED, thought "oh how cute", and turned the thing on. OW!

So, now I have it internalized that LED's are _different_ in the 21st century.

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www.wescottdesign.com
Reply to
Tim Wescott

outside. With the beam on its highest regular setting coming from eye level, I could see what looked like moderate to heavy snow with the "snowflakes" probably being teeny tiny little specks of pollen.

Reply to
John Doe

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