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.

145 Typical lumens from 700mA @ 3.6V, or 58 lumens per watt. The LED is a surface mount chip 3.1 x 4.6 x 2.1 millimeters in size. A thin strip of 12 of these chips puts out light comparable to a 100W tungsten lamp but only uses 30W.

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.

--
*If your feet smell and your nose runs, you're built upside down.  

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

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

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.

Well actually I wonder about that. Especially replacements for those 'low voltage halogen' types like these.

There's not actually any easy way to lose the heat. The 'enclosure' is very small.

I'm not so sure about the quickly bit.

Graham

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

No fair! >:) You try fitting a CFL in there. That's why you're pulling teeth out of the biting argument in favour of LED's isn't it? Most of the time in this thread you're advocating CFL's, so this is a spurious issue.

Actually, the Cliften Suspension Bridge in Bristol has its chains entirely lit by exactly the type of LED-based lamp that replaces little tunsten halogens. There are three emitters per lamp. The lowest is too high to get a good look at, but they appear to be Cree or Luxeons in small parabolic reflectors. Sure, a bridge doesn't have many cooling problems most times, but those 'chains' are mighty plates of iron, and on summer nights they are hot. Doesn't stop those lamps working though.

Lostgallifreyan wrote in news:Xns9968D2D4113A1zoodlewurdle@140.99.99.130:

That is so embarrasing I have to correct it. 'Clifton'.

To be honest, I'm not actually advocating any specific technology. I am however very interested on Philips new compact 'CHLi' halogens.

I have seen LED 'replacements' for that GU10 type touted, but it's clear they must have very much lower light output.

Graham

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

I'm keen on the developments in halogen lamps too. They have a light quality I consider second to none. I hope broadband phosphor mixes will be improved, but they still don't work like a small efficient halogen does.

I need to stop now, want to watch Minder. :) I need a rest.

145 typical lumens at junction temperature 25 degrees C for the highest brightness rank in the datasheet. Now, what about with a heatsink temperature of 35 degrees C and for the highest brightness rank in the Future Electronics website? 30 watts into these means probably about 25 watts of heat. Hmmm, what if you mount a dozen of those onto a heatsink the size of the tip and heating element combined of a 25 watt soldering iron? What would the heatsink temperature reach then? What does the datasheet say performance is at that temperature?

With a good size heatsink to stay at a comfortable temperature with 25 watts, I don't see it looking like a universal incandescent or CFL replacement just yet.

That I believe!

- Don Klipstein ( snipped-for-privacy@misty.com)

No, they use a different phosphor made for LEDs. Color rendering of white LEDs is more like that of "old tech" halophoaphate fluorescents than like that of CFLs. At least the color rendering index is somewhat better than that of "old tech cool white".

- Don Klipstein ( snipped-for-privacy@misty.com)

White LEDs are nonlinear, generally with efficiency maximized at some fraction of rated power.

When an LED or an LED cluster has to dissipate 20 watts of heat, it will probably have to be bigger than a CFL of same power input.

There are some high power IR laser diodes more efficienct than LPS. Other than those, laser diodes are less efficient than most sodium lamps.

Phosphors have a loss. I expect the ultimate in LED efficiency in the future will have at least some of the light being the radiation produced by the LED chips, rather than by phosphors.

- Don Klipstein ( snipped-for-privacy@misty.com)

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Ok, but try thermally coupling a CFL, or any part of one, to a heatsink. LED's and their drivers are much more easily adapted to use existing structures to carry the heat away. That's why they can occuppy smaller volumes. This is actually done, I mentioned the Clifton Suspension Bridge in another post, that's covered from end to end in them, they're tiny, and extremely bright, and they use a small metal cowling to carry heat from the emitters. They're not 20 watts, more like 10, but the total size of the lamp is similar to a low-volt halogen, far smaller than an 11 watt CFL.

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

I think so too. And I hope so. Phosphors don't allow colour mixing, and that's one of the biggest strengths of LED's.

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Ok. I thought more laser diodes were but never mind.. Aren't most class 3B visible red diodes around 20% efficient or more though? That still leaves a lot of headroom. Tungsten is often said to be 1% to 2% efficient at making visible light. So a 100W incandescent 17 l/W at 1% to 2% places the Cree XR-E's 50+ l/W at 3 times that, up to 6%. These are loose figures but they suggest that if LED's reach efficiencies like DVD writer diodes, maybe 3 to

4 times the current efficiency can be had. (Not including phosphor losses, but including LED driver losses). These figures are assuming Imax, 1A per emitter, if LED's become cheap enough to double the emitter count and drive each at 500 mA, the efficiency will go up by 50% or more.

Wikipedia says 2.6% for the ubiquitous 100W tungsten filament bulb and 3.5% for quartz halogen.

Graham