Musings on the progress of LED lighting.

[Ian Stirling]

Back in 2003/4/5 I made some posts to this group on the topic of LED lighting, and I thought it was interesting to come back and reflect on the state of the art.

Over the past few years, prices of high power LEDs have crashed, and the efficiency of the lower end of the scale has risen.

- for example - 12W LED for 12 quid - with 620 lumens output or so - about 50lm/w, comparable with the lower end CFLs.

- at the higher end - if you use 12 of these, you get 12W, but with perhaps twice the brightness.

One of

- a universal power supply - 10 of the above, and you get a 1000lm light, that uses maybe

12W - practically as efficient as a linear fluorescant, and much better than a compact one, as bright as a 100W conventional light, for around 40 quid, and that's not even in volume. If you're making a few thousand, you could probably sell them for that.

Admittedly, at the moment, the light colour from the above is pretty horrible, and has almost no yellow.

At the moment nice warm white ones are about half the brightness.

So - some way to go, but it's catching up fast to CFL.

The dealextreme site (only a customer) also has other fun stuff. I plan to take one of the above 12W LEDs, one of

and do a starscape of the brightest 300 or so stars.

Also experimenting with use in steps.

Pour little bit of concrete, put some fibers on top, pour bit more, repeat until mold is full, then clean off with angle-grinder to expose the ends.

I'm also trying to source high refractive index spheres - as used in reflective paint - to make a virtual sky light.

[Andrew Gabriel]

They're called ballotini (Italian: "little balls";-) if that helps you find them. Not sure they're actually high refractive index though.

[Mary Fisher]

...

If 'conventional' lighting had always had a blue cast then new, energy efficient lighting was yellow, I suspect none of us would like it ...

Mary

[Bruce]

That's more or less what happened with electric street lighting.

First they used incandescent bulbs that gave a reasonable impression of white light. They weren't very bright, and used quite a lot of power. Then someone invented/developed the sodium discharge lamp, which was brighter and used much less power, and street lighting went horribly yellow.

After that came the mercury discharge lamp (blue/green) and the high pressure sodium discharge lamp (yellow/pink).

[John Rumm]

Its the discontinuous spectra that is more objectionable that the actual colour cast.

[Mike Tomlinson]

In article , Ian Stirling writes

2800mA? That's got to be a misprint, surely?

IMO, it's unusable for room lighting. OK for point work (saw some used in a museum recently for display case illumination and they were ok there.)

I can't stand the light from LEDs or CFLs. Moved into a new house last year and the place was infested with CFLs. All since consigned to the bin and replaced with nice incandescents.

[Mary Fisher]

As you said, it's a personal preference.

We have LEDs on our landing - only used at night of course - and we love it, it's like the (full) moonlight we get through the windows.

I'm looking forward to more powerful ones for spot lighting in living rooms - which means every room of course because we're alive :-)

Mary

[Dave Plowman (News)]

It's not so much the 'cast' of the actual source when looking at *it*, but more the sort of light it produces. Ie, what it does to other colours. And the two are very different.

[Dave Plowman (News)]

Yup - I recently tried some 'warm white' LEDs which produce an even worse spectrum than the 'blue' ones.

[Dave Plowman (News)]

I doubt you do very much in the landing apart from walk through it.

The requirements for decent lighting are different than just safety illumination. And it wouldn't surprise me if LED can *never* satisfy this.

[Andy Champ]

I'm quite happy with the colour on the monitor I'm using now - and that's just three colours.

I also see no reason why an LED light shouldn't use many overlapping phosphors to give a reasonably flat spectrum.

Andy

[stuart noble]

I gather from a mate in the industry that the refrigerated display sector are pushing development in this area so they can continue to control how food looks in the supermarket.

[Ian Stirling]

You'd be wrong - certain classes of warm-white LEDs have a spectrum insignificantly different from tungsten - apart from IR. However, these are _lots_ less efficient than normal ones.

[Mary Fisher]

I know and that's what I'm talking about. Coloured light is cast on objects which appear differently from when light is cast on them from a different source.

Mary

[Dave Plowman (News)]

Indeed. And without reasonable efficiency there is absolutely no point in them.

[Dave Plowman (News)]

It isn't just three spot frequencies.

They don't use phosphors.

[Rod]

I thought they did - in making (some) white LEDs - using a colour phosphor to "convert" blue light.

I guess that is sort of outwith the LED part of the LED (IYSWIM).

[Ian Stirling]

But I do note that this is a really young field - well under a decade for decent power LEDs, with an efficiency of over halogen light.

Claiming 'never' is perhaps a little pessimistic.

[Ian Stirling]

They do.

99.9% of 'white' LEDs are in fact a blue LED, with a varying sort of phosphor on the top, that lets some of the blue through.

See page 5 of

, for a typical 'white' LED spectrum - the variants are assorted 'colour temperatures' - byt these are dramatically misleading as there is a huge gap at cyan-leafgreen.

The 'red' curve in this is 'warm white'.

There are better -

, see page 8 fig

2A for a spectrum that looks really quite close to tungsten.

However - these are one fifth as bright as the bluest whites on the first datasheet.

It'll get better.

[Ian Stirling]

As an aside, there is an argument for tungsten being semi hard-wired into the brain. Maybe not a good one. But as we age, and more significantly as we are exposed to solar UV, the amount of blue light recieved by the eye drops significantly.

This is just what happens when you use tungsten to illuminate things.