back to article The amazing magical LED: Has it really been fifty years already?

Next time I hear Coldplay festively crooning "May all your troubles soon be gone, Oh Christmas Lights keep shinin' on," I'd like to think that far from lamenting some lost love, they're paying solemn tribute to the humble but illuminating LED. The Light Emitting Diode celebrated its 50th anniversary this year. It's easy to …

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Re: Every one already?

Well sometimes a traffic light fails, intersections sometimes are only give way or stop and not lit. If you can't see any light at all any reasonable motorist would assume a traffic light fault and proceed with extreme caution treating it as a give-way, surely?

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Re: Every one already?

It's not true. Looks out side and sees a non LED signal lights.

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Anonymous Coward

Re: Every one already?

Even here in my Indian home city, the traffic signals are, I think, LED. One sad thing: the old ones used to have the word RELAX on the red light: they don't do that now, so nobody does.

On the colour temperature issue, I just replaced most of the cool white fluorescent tubes in my house with warm white. I find it much more restful and soothing ...but is it natural? It is certainly nothing like the hard tropical sunshine outside, so no, in that sense it is not, but it makes my house feel more like a home and less like an office.

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Re: Every one already?

@Heyrick: "This problem was solved eons ago on the railways. Red, being the most important signal, goes at the bottom. Cannot be obscured by a heap of snow, unless the snow rises to the level of the signal in which case it is unlikely the line will still be in use."

There's one slight problem with doing that. Road vehicle drivers can be red-green colour blind so position is crucial. Train drivers must have good colour vision.

Interestingly LED signals on railways save more cost because three colours can be incorporated into one aspect, much like searchlight signals but without the mechanical filters. Also incandescent lamps were expensive because they had dual filiamnets for redundancy plus the necessary current detection and switchover circuitry. No doubt there is still some proving for LED signals but you don't need to duplicate the LEDs because they're not all going to fail at once.

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@heyrick

This problem was solved eons ago on the railways. Red, being the most important signal, goes at the bottom. Cannot be obscured by a heap of snow, unless the snow rises to the level of the signal in which case it is unlikely the line will still be in use.

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Er...what? Perhaps I'm missing something, but I fail to see how having the red signal on the bottom makes any difference whatsoever to whether it can be obscured by snow. Can you explain why this makes a difference on a railroad?

The issues noted in the US are due to wind blown snow freezing onto the face of the signal. With incandescent bulbs they had enough waste heat to keep the surface of the glass above freezing (except maybe in places like Nome) so this never happened. With the more efficient LEDs, a heavy wet windblown snow can stick to the surface and prevent you from seeing the signal at all, regardless of what color it is or whether red is at the top, bottom or middle.

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Re: Every one already?

Road vehicle drivers can be red-green colour blind so position is crucial.

Or pattern, although that would need a new traffic code to go with the differently-placed lights. Like a red X for stop, a yellow - for impending stop, and a green O for go.

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Re: @heyrick

Perhaps I'm missing something, but I fail to see how having the red signal on the bottom makes any difference whatsoever to whether it can be obscured by snow.

Signals, and traffic lights, have these shadow shields that (try to) keep direct sunlight off the glass. Snow collects on them, and obscures the light above.

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Re: Every one already?

In colder climates even incandescent bulbs aren't warm enough and enclosure heaters have to be used.

I'm sure the canadians can sell them a few thousand heatpacks.

The problem mentioned isn't new, or exclusive to led signals - and if a signal has no lights showing, common-sense plus road rules worldwide say "approach with extreme caution"

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Re: Every one already?

The problem mentioned isn't new, or exclusive to led signals - and if a signal has no lights showing, common-sense plus road rules worldwide say "approach with extreme caution"

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That's great, but only if you see the signal pole and realize this. You may not at night, or perhaps when it is snowing, raining, or foggy.

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Re: @heyrick

@ Doug S: "Perhaps I'm missing something, but I fail to see how having the red signal on the bottom makes any difference whatsoever to whether it can be obscured by snow."

Fow what it is worth... here's why red comes at the bottom (as previously noted by a commentor, I'm just giving you a pretty picture to look at <g>):

http://www.southernelectric.org.uk/features/galleries/snow2010/img/csm450028winchfield090110.jpg

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Re: Every one already?

If you Google it, the articles that appear in the results would appear to support the assertion, if not address it directly. For example: "Federal transportation officials have been pushing local governments for several years to switch to brighter, more energy-efficient LED traffic signals." -2010

In what way does that support the assertion that every traffic signal has been switched to LED? The US federal government spent years pushing the metric system, the 55 MPH speed limit, avoiding tobacco products, and a handful of other things that have not found universal acceptance.

The article is flat-out wrong on this point. It was a bizarre claim to make.

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PT

Re: Every one already?

True, it is not EVERY light. Local governments have enough budget problems already, and can't afford to put out a lot of capital now to save money later. This problem has been ingeniously tackled by the lighting manufacturers, though, who (in my city at least) upgraded many incandescent traffic lights to LED at their own expense in exchange for several years' worth of the money saved on the electricity bill.

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Re: Every one already?

I live in Raleigh, NC, USA. There are still signals that have not been converted, but my unscientific survey would say at least 90% of the lights I drive by have been converted. An article in the local rag here years back ran the power consumption numbers, and noted that the (then) very pricey bulbs would pay for themselves in electrical savings in well under a year. Naturally, our taxes were not adjusted downward a year on, so either the cost savings was not realized, or we have politicians in our midst. Me fears the latter.

So no, the claim of the author was inaccurate, but every time a bulb blows in a signal there is one less tungsten traffic light. BTW -- we are somewhat slow to adopt new technology in the South. A generation has to die out before we move ahead one step.

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Semiconductor diodes always confuse people

"...adding a battery with its positive end connected to the free electron 'n' side of the diode, and the negative end connected to the extra holes 'p' side, things change. The 'n' side electrons are attracted to the positive electrode, and the 'p' side holes are attracted to the negative electrode."

That is a reverse biased diode; no current flows and the depletion zone increases in thickness. As you say :

"No current flows because both the electrons and the holes are moving away from each other. But the depletion zone increases, ......"

But then ...

".... and the interaction between the electrons and the holes releases energy in the form of photons - which generate light."

No. There is no interaction because the electrons and holes move away from each other to opposite ends of the diode, like shy boys and girls at a dance.

It is when the diode is forward biased, with the battery anode connected to the 'p' side and the battery cathode connected to the 'n' side that current flows. Electrons are injected into the 'n' material and flow towards the depletion zone, thus reducing its thickness; 'holes' are effectively created in the 'p' side and flow towards the depletion zone (reducing its thickness to zero), where they combine with the electrons - the resulting energy being converted (partly) to light.

Wikipedia has a good diagram of this:

http://en.wikipedia.org/wiki/File:PnJunction-LED-E.svg

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(Written by Reg staff) Silver badge

Re: Semiconductor diodes always confuse people

Whoops. The article's Semiconductor Physics 101 has been tweaked. Thanks for the feedback.

C.

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FAIL

Reverse biased diodes don't pass (significant) current.

So where is the energy coming from to create the light?

Every time one has lit up for me, it's been forward biased, with a ballast resistor or other arrangement to ensure a sustainable current level and avoid self-destruction.

As I've been tinkering with them since their infancy I think I've got them the right way round.

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Re: Reverse biased diodes don't pass (significant) current.

Yep, forward-biased makes them glow, in simple applications you use a series resistor to set the current/brightness to the desired level. The resistor often consumes more energy than the LED, hence the use of more sophisticated controllers in lighting applications.

I'm surprised no-one has mentioned the Q-word - Quantum. LEDs are one of the most visible (ha!) demonstrations of quantum physics. The real magic is when the recombination takes place; electrons drop to a lower energy level, emitting the excess energy as a photon (a particle of light). The frequency or colour of light is determined by the energy of its photons, and the exotic materials in LEDs are chosen to get the right "energy gap" to get the required colour.

The macro world we sense has continuously-variable energy levels (e.g. the orbit of a planet, the speed of a car, etc) but at the atomic level only certain discrete energy levels are possible, hence the emission of a very defined quanta of light energy from recombination, and therefore the tight spectral purity of LEDs.

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OLED energy efficiency? Hmmm...

"Our monitors, televisions, laptops, smartphones and tablets are now capable of delivering a picture quality that makes us grin without forcing us to recharge often enough to make us groan."

My experience with OLED screens is that they are no less energy-hungry* than backlit LCD screens, so while they do have many benefits, energy efficiency is not really one of them at this time. Plus, the well documented issues with producing durable and cost-effective OLED screens of larger sizes pretty much means OLED "monitors, televisions & laptops" remain a possibility for the future, rather a reality today.

* OK, I know that in lab conditions that, compared to a similar LCD, the OLED will consume less energy showing a dark image and more showing a light one, but in general this usage evens out on average. I dare say that with an optimised (i.e. dark) UI and apps, OLED could be made to go much further.

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Anonymous Coward

Bored of Blue LED now!

Just because Blue was difficult until 10-15 years ago, it's been "trendy" for some time now to light things up blue.

It's horrible, it hurts my eyes, it's unnatural, it doesn't look nice, it's not trendy any more, PLEASE STOP IT, world!

That is all.

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Re: Bored of Blue LED now!

In the 70s and 80s, high technology came with a wooden veneer and lots of lovely knobs, flick switches and dials.

In the 90s, it was CHROME, CHROME EVERYWHERE.

Now, high technology glows blue.

It's just one of those things. Next it'll be touch screens on everything.

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Headmaster

Re: Bored of Blue LED now!

It's not "Bored of" it's "Bored WITH".

I hate "Bored of". It's horrible, it hurts my eyes, it's unnatural, it doesn't look nice, it's not trendy any more, PLEASE STOP IT, world!

That is all.

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Anonymous Coward

Re: Bored of Blue LED now!

Green is the eye's most sensitive part of the spectrum. Blue is one of its much less sensitive areas. However for most people there seems to be a psychological attraction to "pretty electric blue" - as every Igor knows. That makes some traditional sources dangerous attractions because of their UV content (not standard blue LEDs)

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Anonymous Coward

Re: Bored of Blue LED now!

A neighbour has what appears to be a matrix of powerful blue LEDs (or lasers) in his back garden. Presumably an intruder detection system. Even an edge scatter seen through a house window at 30 metres plus feels painful.

Anyone any idea what they might be? No point asking the neighbour - he seems to treat such installations as his divine right.

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Anonymous Coward

Re: Bored of Blue LED now!

Nope.

I use blue for power/access indication and background lighting (when not using white, that is). Red is alarm, green is OK, blue is live.

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@AC 12:27

I doubt the string of blue LEDs your neighbour has is anything to do with the workings of a security system - other than a visual warning - because PIR sensors rely only on heat and 'night vision' security cameras usually rely on IR light.

Much like this laser scanning security device someone developed which does absolutely nothing other than provide a 'light show' to warn potential burglars that there (probably) is a high tech security system in the premesis - https://www.youtube.com/watch?v=GnH95uzQPOo

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Blue LEDs as ornaments

And Jeebus, I walked my dog past some houses the other day, and couldn't help but notice that people had decorated their indoor Christmas trees with blue LEDs. I can't stand the things, but it seems some people like them. These weren't the sort of houses that are enthusiastically covered in plastic reindeer and inflatable snowmen, either.

Bad design: Yesterday I bought a car cigarette-lighter >USB power adaptor from a garage... it was fitted with a blue power indicator that was so bright it would distract any driver. Not good. Still, it was easily fixed with the Duck-tape that is kept in the car.

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Duck tape

Since we have so many pedants around, I am surprised tnat no-one has pointed out that Duck Tape is a brand of duct tape. In the Uk we call it 'Gaffer' tape, after the head electrician in theatres, renowned for using it to solve all problems!

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Re: Duck tape

Indeed, branded Duck tape's the best. The cheaper chinese copies are rubbish...

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Re: Duck tape

Proper 'Gaffer' tape is different them Duck/Duct tape (and much more expensive).

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Re: Duck tape

I'd buy something from Advance Tapes or Le Mark over Duck any day.

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Re: @AC 12:27

Indeed. Where I work, there was classified technology on the premises. The whole building was protected (during that period) by the Military police (although we are not a military organisation) and a security system using lasers. The only visible sign of the security system were 8 foot tall smoked glass towers placed at regular intervals throughout the grounds, along with a *lot* of security cameras.

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Re: Bored of Blue LED now!

Anything with blue LEDs is by definition cool. You obviously just need more of them.

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Headmaster

Re: Duck tape

Sigh, here we go again. Even the Wikipedia article gets all out-of-shape over "Duck" and "duct" tape, while correctly describing the function of each.

The sticky, hand tearable stuff that you repair the world with is Duck tape. This follows on from the military stuff used to hold ammo boxes shut and keep the wet out.

If you used Duck tape on a duct, it would quickly dry and crack, especially if the duct carries warm air. Duct tape does not have the awesome properties demonstrated on Mythbusters. It does, however, have adhesive that continues to work at higher temperatures, and is resistant to cracking. Some varieties incorporate a foil layer to improve airtightness.

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Unhappy

Re: Bored of Blue LED now!

It's not "Bored of" it's "Bored WITH".

I hate "Bored of". It's horrible, it hurts my eyes, it's unnatural, it doesn't look nice, it's not trendy any more, PLEASE STOP IT, world!

That is all.

it is right up there with "try and do it" which to my eye reads as "you should try to do it AND do it "

what is wrong with " try TO do it " ?

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Stop

Re: Bored of Blue LED now!

I have two words for you.. "black ash"..

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Re: Duck tape

Indeed, branded Duck tape's the best.

Well, if you ignore Nishiban.

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Coat

Re: Bored of Blue LED now!

In the 70s and 80s, high technology came with a wooden veneer

Indeed. I do miss those rosewood- and palissander-sided mainframes of yore. Painted sheetmetal is so crude by comparison.

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Painted sheetmetal is so crude by comparison.

Now it's black plastic with small off-white text that can't be read from more then 6" away.

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Joke

Re: @AC 12:27

I bet eight-foot tall military policemen would also have been a deterrent to any potential intruders!

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Re: Bored of Blue LED now!

In the 70s and 80s, high technology came with a wooden veneer and lots of lovely knobs, flick switches and dials.

In the 90s, it was CHROME, CHROME EVERYWHERE...

Eeehhhh, maybe, maybe not, depending on where you lived, I guess.

For me, the late '60s/early '70s had the cool wooden veneer cases with lots of backlit FM dials, and those edge-lit electroluminescent signal/VU meters, and yeah, more knobs and flip switches than you could shake a stick at.

The mid '70s came along and all that stuff turned into red LEDs, except perhaps for VU meters, most of which still used needles. Still lots of fake wood until the late '70s and early '80s, when we suddenly started seeing all the chrome and fake brushed aluminum we could take. The early '80s also gave us really cool electroluminescent VU meters along with LEDs everywhere in our tape decks -- or, as my sound geek pals called it, "Tokyo By Night". (Interestingly, I don't remember a whole lot of LCD displays on stereos back then)

In the '90s every display in every sound-system component I saw turned into blue and amber LEDs, even the VU meters, and with lots of those little pushy-touch switches -- and lots and lots of black. Cases, knobs, display bezels, everything. The sound components on the table next to me -- tuner, amp, CD player -- were bought as a set around 1991 or '92, and it's just a big-assed stack of black. The tape deck was bought in the mid/late '90s and it, too, is a big ol' black slab.

...It's just one of those things. Next it'll be touch screens on everything...

Yeah, even touch screens on things which aren't really suited for touch screens, sadly. Still, I have seen some consumer electronics and appliances that have benefited from having little EL screens with little bare-bones GUIs running on them. We just got a new printer/scanner/copier combo at our house, and it has a little screen on it about the size of a video iPod screen with four or five buttons around it that let you click and scroll through the menus. Really well done, actually.

Actually -- granted, it's a long shot and rather silly -- I'm hoping the next trend in stereo components is brushed aluminum and wood cases with little nixie-tube displays for the tuners. I know you really need LEDs or LCDs to build a proper handheld calculator, but nixies still have a slight edge in "coolness".

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Re: Bored of Blue LED now!

...However for most people there seems to be a psychological attraction to "pretty electric blue" - as every Igor knows...

Huh, never thought of that. Yeah, blue does look kinda cool, but I've never been that into it one way or the other. It could be a generational thing; the first devices I owned with LEDs in them in the mid '70s -- my first digital clock radio, my first digital watch, my first handheld calculator -- all had red ones, and so I came to associate that authoritative red LED glow with "high-tech future".

Of course, the famous Apollo Guidance Computer was already bucking the trend with a green display.

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Re: Bored of Blue LED now!

Blue light in a bedroom is a fast way of getting a rotten night's sleep. That was fairly well known a long time before blue leds came in the scene.

Personally I hate excess use of blue because the it's harder to focus on (the eye is optimised for green-red) and tiring after a while.

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Re: Bored of Blue LED now!

"A neighbour has what appears to be a matrix of powerful blue LEDs (or lasers) in his back garden. Presumably an intruder detection system."

Um... FAIL? Surely the point of sensors is that they see you before you see them - hence the bank heists in movies using special vision goggles and spray-can smoke, etc... I mean, what good is pointing out the security system? That'll just tell potential burglars where to avoid - like land mines with little pink flags on top...

BTW, FWIW, I like blue LEDs.

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Vic

Re: @AC 12:27

> to warn potential burglars that there (probably) is a high tech security system in the premesis

Or, more likely, to inform burglars that there probably *isn't* a high tech security system on the premises...

Vic.

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Home & Work Light?

It's rubbish for those as the spectrum is too poor. Missing colours. It's not even as good as CFL in which the phosphors work better. CFL even is poorer than Halogen for colour rendition.

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Re: Home & Work Light?

LEDs work absolutely fine for us - we have replaced nearly all lights in the house (apart from a few remaining CFLs) with LED and the light quality is wonderful in my view. I have used the "Warm white" LEDs (around 3000k nominally) and the colour rendering is very much better than CFLs and about the same as halogen - the problem with CFLs always used to be certain foods (such as red meat) just appeared the wrong colour, but this problem does not occur with LEDs.

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Re: Home & Work Light?

I agree with Mage here. Ultimately there is no such thing as a true "white" LED - they are essentially integrated green, red and blue units in the proper balance to approximate white light to a human eye. However, that lack of continuous spectrum does cause subtle colour issues at times - I think I've commented here before that it is virtually impossible to distinguish brown and violet resistor colour bands under LED lights. It only takes one or two expensive, time consuming mistakes caused by that kind of issue before you are left vowing never to trust LED lighting again.

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Boffin

Re: Home & Work Light?

"Colour rendering is very much better than CFLs and about the same as halogen"

Nothing like. LEDs have gaps in the spectrum. You are confusing "Colour Temperature" or how Neutral the colour appears looking AT it or neutral surfaces to the accuracy of colours seen with the light reflected from objects.

Certain shades of Cyan will go green or blue. Other colours will go "muddy" or even grey.

CFLs and Florescent tubes have spikes and some gaps, but due to the direct plasma and mix of UVA and UVB wavelengths a mix of phosphors can give much better light than the Blue/Violet/Near UV of an LED. White LEDs don't exist, they use phosphors. R G B LEDS can "mix" to give illusion of almost any colour, but are the very worst illumination source as it's near monochromatic Red, Green and Blue. Coloured objects will appear the wrong colour and it's possible to have a brightly coloured object appear dark grey or a darker spurious colour under RGB light than under CFL or even phosphor based White LED. It will be most natural in overcast sky mid daylight and next most natural (but orange enhanced) under Halogen. Only Halogen and Tungsten can be colour balanced later in Photo Editing. With RGB or White LED the colour information isn't in the photo or video, it's lost.

Cameras use three or more broad overlapping responses to generate the RGB data for later colour image (which can then use monochromatic RGB). But you need broad spectrum lighting with no gaps to create the viewing illusion accurately.

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Boffin

Re: Home & Work Light?

they are essentially integrated green, red and blue units in the proper balance to approximate white light to a human eye.

They're not. "White" LEDs are essentially UV or near-UV (single-colour) LEDs with fluorescent coating. Some coating mixtures are better than others at providing a not-awfully-gappy spectrum, but it's still discontinuous, like, well, fluorescents. Another issue is that the coating degrades with use, although it tends to keep up well beyond the life that most incandescents have anyway.

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Re: Home & Work Light?

Halogen is excellent for colour rendition - only xenon is better. Turn up your wattage.

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