Thoughts on LED lighting

[Jeff Mowatt]

Something I'm considering seriously given the potential for energy reduction.

A feedback comment from a customer on one of the supplier sites mentioned that he'd been able to use these 12v units connected to a car battery in a stable without any electricity supply.

This got me thinking. Considering the frequency of power cuts where I live, might it be a good idea to introduce a backup battery into the circuit, with overcharge protection naturally?

What I don't know is whether this would be in violation of any safety standards, or even if there are any standards for this new technology.

[Dave Plowman (News)]

There isn't any, really. Not much to pick and choose between those and fluorescents.

Same as fluorescents. But they tend to give a more usable light.

Can do. But you could equally as easily do this for mains stuff, or other LV technology.

At the moment it's just yet another new fad. Some uses for specialist apps. But no 'killer' yet.

[Peter Parry]

They use more energy than a fluorescent lamp for equivalent light output.

It's just a 12V lamp made up from a LED cluster, nothing unusual about it. Used off a 12V battery a good LED lamp will probably have better efficiency than a caravan type fluorescent with a cheap built in inverter but there won't be much in it.

A simpler solution might be to use something like

a maintained emergency light such as

with a modification to the mains fail side to make it switchable (as it is the battery powered tube comes on automatically if power fails).

[Guy King]

The message from Peter Parry contains these words:

The current record for LED efficiency is 132 Lumens/watt - something fluorescent lamps struggle to approach.

Generally available white LEDs achieve 65 Lumens/watt. As far as I can find, CFLs range about the same, from 45 to 70 lumens/watt.

So - while a year or three ago LEDs were less efficient than CFLs, they are now comparable, with the likelyhood of them being much more efficient than CLFs in the near future.

[Ian Stirling]

Not for white. You may as well claim 180lm/W as a figure to compare with (yellow low-pressure sodium, as used to be seen lots in streetlights).

I assume you are talking about LEDs like the cree XLamp 7090 XR-E LED.

This does indeed claim boldly on the website that it gets 70lm 'typical'. However. This is with cooling, in 99% of environments, as it only hits that with the point the LEDs are soldered to at 17C, neglecting any further temperature rise in the heatsink.

At a Tj of 60C or so, which is a heatsink temperature of 50C, which may be just about packagable into a normal CFL bulb shaped device (without a fan), you're down to 90% of this figure.

Add a 90% efficient power supply, and we're at 80%. For 70lm/w, this is 56lm/W. However, they do not guarantee that you will get 70lm, the minimum brightness bin is 62lm/W, which drops it a fair way.

The other problem...

Now, look at the spectral distribution of this LED. It's _horrible_ for lighting - most of the light comes out as blue, with some yellow to make it whitish. Putting in a better phosphor mix drops it quite a lot.

Getting there, but quite a way to go yet.

[Dave Plowman (News)]

Be interesting to know the spectrum output of that LED versus the florry.

Again, wonder how this output is measured? A fluorescent gives substantially 360 degree light output. LEDs don't.

[Guy King]

The message from Ian Stirling contains these words:

Yes, for white.

[The Natural Philosopher]

Thats down to lenses and diffusers.

actually there are some electroluminescent materials around that look set to challenge both technologies in a few years time..likely to turn up first behind the LCD display on your phone etc. IIRC the conversion efficiency as better than LED, not quite so good as top notch fluorescent, but close to it.

[Guy King]

The message from "Dave Plowman (News)" contains these words:

Doesn't matter - it's how much light comes out per watt in. Fluoro's

360° can be a right PITA, as much of it hits the fitting instead of going where it's wanted. With LEDs you can shove it where the light doesn't shine.

[Jeff Mowatt]

Indeed, and if the pioneers of the CFL technology are now making big investment in LED production, that's indication enough for me that they're viable.

Meanwhile I may buy some tealights!

[The Grim Reaper]

I thought the whole point of LED light units/clusters was that LED's last a lot longer than conventional bulbs/CFL??? Or am I thinking of something totally different?! :-) ______________________________________ The Grim Reaper

[Dave Plowman (News)]

LEDs when used as panel signalling lamps have a near infinite life. Not quite the same when you up the current to get some useful light out of them, though.

[The Natural Philosopher]

Agreed. Lifetime of semiconductors is very much heat related..apart from heat/cool/expansion mechanical seal fracture stuff, the doping gradually migrates and diffuses..transistors do 'age'..and very rapidly as the junction temperatures increase to near the critical points - around

175-200C for silicon, less for germanium,, dunno with gallium.

Nevertheless, not used continuously I would expect 20 years or more life out of a LED.

[Dave Plowman (News)]

There's a surprising number of cars around with faulty LED third brake lights. Of course it may be the resistors.

[Tony Williams]

My handbook says that repairing the third brake light LED cluster is a main-agent job only, and I suspect it would be a complete replacement. Perhaps that's why they don't get seen to. :(

[Guy King]

The message from Tony Williams contains these words:

I bet it's fairly simple inside.

[Adam Aglionby]

Cheap fluro can have terrible colour rendering, old halo p0hosphates could go as low as 55 CRI , good fluoro will be 90+ CRI, halogen light and daylight are CRI 100.

Lumens is a measure of total light output regardless of direction, its measured in an integrating sphere. Lux is delivered light in a given direction and Candela is directed light where the number increases with narrower angle, hence some of the ridiculous Cd figures you see for some LEDs, narrow beam angle high Cd numbers.

In the manufactures very well chilled labs perhaps. Remember also lumen depreciation like fluros lamp dosen`t just die its output drops over time, Lumileds puts Luxeon white dropping to approximately 70% after

50K hours, in ideal conditions.

Adam

[Andy Wade]

Cheap indicator LEDs dim with age far more than many people realise. A demonstration can often be seen on a computer keyboard. If you keep NumLock on all the time, but only use CapsLock now and again (and ScrollLock never) put them all on and compare the brightness of the LEDs.

[Guy King]

The message from Andy Wade contains these words:

I can't see either of mine under the dirt.

[mcbrien410]

About 30 years ago, my brother was involved in the installation of small wind turbines of about 2kWatt size. This was in Switzerland at an area called Little Siberia. It is a farming plateau. The wind mills just provided 12 Volt lighting for farm buildings. Their saving was not electrically based but their INSURANCE premiums dropped because they were using oil based lighting previously. The white mans burden, INSURANCE.

Chris.