LEDs as lamp replacements

Don't believe everything you read.

Experience is the best teacher.

In other words, LEDs suck for bright light sources.

However, the hype is good for selling them to fools over the TV/Internet. Like that one guy selling LED light bulbs on TV (USA). He doesn't explicitly say that they're bright as a lightbulb, but they are in a lightbulb package and used in the commercial as if they were a lightbulb. Some people probably fall for that.

Right, but pointless except for low light applications.

John Doe wrote in news:7GGji.18519$ snipped-for-privacy@newssvr14.news.prodigy.net:

In your infinite wisdom, how do you explain this?

NIST confim the brightness, so you don't have to believe the 'hype', you only have to ask a few basic technical questions: How efficient is it? Is there enough light to fit purpose at given cost?

"LED luminaires can only be considered high efficacy if the LED can be tested (according to UL) to be at least 40 lm/W on the line voltage input side of any power supply or other device.? Otherwise the fixture is not considered high efficacy." Source:

Light Type: lm/WW CRI Life (hrs) Incandescent 17 100 3k Halogen 20 100 10k Cree XLamp 7090 XR 48 80 >50k T12 flourescent 60 75-85 20k Metal halide 70 70 20k Cree XLamp 7090 XR-E 70 80 >50k T8 flourescent 74 75-85 20k High-pressure sodium 91 22 20k Low-pressure sodium 120 5 18k Source:

Even if you lose nearly half the light you can still claim high efficiency to UL standards given the 95% efficient power converters made to run LED lamps. It would be a poor luminaire that lost that much.

As for actual light output, newer LED's put out 176 lumens or more. That's still a tad short of what's wanted in many cases, but not by much. 7 to 10 emitters would match a standard 100W incandescent (7 for the 240V type, 10 for the 110V type). Given that the cost of the first CFL's was around £26 in the UK, maybe £40 in todays money, that puts LED's in a good position, you can get a lot better device for a lot less than that, even now, and it's improving fast, a lot faster than the time CFL's took to develop, and there are probably more ways to cut costs without sacrificing safety.

It would take only a fourfold increase in output from a single emitter at same cost to make them compete with any other light source for domestic use, and I think we'll only need to wait a few months for that.

My feelings, too.

Arfa

I bet you'll find that LED has a 7000K or so colour temp. They're not very nice for domestic lighting.

Graham

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

True, I'm not wild about it, but so long as it can improve enough to avoid sharp dips or peaks I don't mind some serious skew toward blue. We can get used to it as we get used to changes in the colour of ambient daylight, which is often close to what LED's already make. The sharper detail from shortwave blues will help decrease fatigue and increase comfort when reading or doing small-scale work. My only current beef with them is the lack of nice rendering of reds. Adding some broadband red centred around

I'm using 8 of the older Luxeon K2 LEDs in a bicycle light. The output is nothing short of impressive. It's brilliant at just 5W of input power. Crank it up to 40W and it puts car headlights to shame.

No. NOT TYPICAL. That's the highest output (most expensive) grade. LXML-PWC1-0080

In 'cool white' i.e, the very blue light with a 6500K colour temp. Not very suitable for domestic lighting.

More like 95 lumens for a warm white, which works out as 43 lumens/W

Graham

That's poorer efficiency than a CFL can manage. Chances are the colour temperature is poor too - if tungsten is your norm.

The colour temperature won't be anywhere near comparable.

In any case don't 'white leds' use the same phosphor method of producing light that CFLs do ?

Graham

Cite please ?

Graham

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Table: Flux Characteristics (Tj = 25°C) Cree XR-E type P4, 80 lumens at 350 mA Cree XR-E type Q4, 100 lumens at 350 mA Graph: "Relative Intensity vs. Current Tj = 25°C)" Line rising through 100% output at 350 mA to >220% at Imax of 1A. Source:

Logical inference is that the P4 can output >176 at 1 amp, and the Q4 can do >220 lumens at 1 amp.

NIST tested an XR-E Xlamp at 350 mA and found outputs exceeding that claimed in the data sheet. They did not measure the output at 1A but they did certify the lumens per watt. Source:

They did not test the output at 1A, or at least did not certify it, but either the LED's die before you manage to push 1A through them, or they can do what is claimed. Even if there is a fall-off with current, the Q4 type will definitely exceed 176 lumens at 1A.

And there is newer XR-E Q5 Xlamp too. Not sure what its spec is though.

Lostgallifreyan wrote in news:Xns9968B2044C7D5zoodlewurdle@140.99.99.130:

Here's one at 82%:

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Higher intensity. Might be nonlinear, as in greater efficiency if you pump them harder. Might be different materials. I don't know for sure though.

Definitely smaller size, so if you're going to be a stickler for full context such as analysis of lumens per watt of actual mains input, you must take all of the context. People have alreay said (rightly) that LED lamps won't have the trouble that CFL's have in fitting most current luminaries. That's obviously important regarding watse and expense.

More: LED's are growing more efficient all the time. It might be that in future these lamps might be directly driven by encapsulated laser diodes emitting near UV to pump phosphors. Laser diodes have efficiencies beyond low pressure sodium, they leave it in the dust. It's likely that this technology will quickly make CFL's look barbarous.

The LED's maximum rating essentially calls for room temperature. Even with room temperature, the LED die will be much hotter. As the LED heats up, the light output sags. Normally, the Luxeons are allready mounted on a piece of aluminum, which looks like a star, or Luxeon Star. With my mounting arrangement, the Luxeon Emitters are back to back, thus need faster heat transfer. The actual size of the heat transfer piece off the LED die is very small, and is electrically insulated with epoxy, so the heat transfer could be improved.

greg

But that's not mains. Nor do LEDs run off a voltage source. You need to control the current.

I very much doubt it. One very important point however is that these need to be driven with a constant *current* not a constant voltage and that's typically a lossier method too.

Graham

snipped-for-privacy@pitt.edu (GregS) wrote in news:f6ttm2$2f$ snipped-for-privacy@usenet01.srv.cis.pitt.edu:

Good point re output drop with heat. It's not so bad though, linear drop to

Even at >120°C the chips put out 70% of 25°C rated output, and I doubt even ten closely packed emitters will get that hot if convection can keep the mounts below 85°C. Ten emitters in a lightbulb's space couldn't even get that hot unless they had less than twice the efficiency of 100W tungsten lamps, and they're a lot more efficient than that, >80 l/W with a claimed industry best thermal resistance of 8°/W.

Any tips for mounting? :) I'll look deeper at the Cree site for guidance, but for now I'm contemplating an anodised heatsink (such as used for 486 CPU) and using a thin smear of epoxy to fix three of them in place along with a small variable-output driver.. That's crude, so I'm keen to hear some better ideas for improvised assemblies.

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Of course it's not mains, I just cited the one example I had, I mentioned mains later. Might be better to read the whole post before answering, it wasn't a big one.

As for current not voltage, that is why I said POWER conversion. That's what LED drivers do, they put out a controlled CURRENT. It is correct to call this power conversion.

Well, I found one and posted about it already in a later post. 82%, Not too shabby. That runs directly off 240VAC.

Now, how efficiently can you convert VOLTAGES?? What's the best efficiency to get say, 240VAC to 30VDC? Take it, whatever it is, then deduct the 5% from the DC power converter I mentioned above. I suspect it can be better than 82% total? I imagine >90% might be had. You say that the conversion to current is the inefficient bit, but that's the task I cited as being done at 95%. That's why I mentioned the DC power converter, because it is relevant.