Musings on the progress of LED lighting.

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

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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

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).

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

In article , Ian Stirling writes

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.

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

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.

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

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.

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

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.

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.

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

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

It isn't just three spot frequencies.

They don't use phosphors.

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).

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.

They do.

See page 5 of

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

There are better -

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

It'll get better.

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.