Boffins get the inside dope, craft white laser

Arizona State University researchers have crafted a white laser – a neat trick since “white” isn't a colour, but a mix of colours. To create a white LED lamp, for example, today's technologies need multiple colour LEDs blended together. Trying to fabricate a single light source that looks white is difficult, however, since …

[Anonymous Coward]

Correct me if I'm wrong, but it appears the key to making this work are the materials in the green center part of the doping. Since cadmium also exists in the red end and sulfur in the blue end, it's less several discrete sets but a broader, more gradual set that makes it less likely to be incompatible.

[John Smith 19]

Sounds like a functionally graded material at the nanoscale.

Clever, but the abstract is too vague to really tell.

Note that by their operating mechanism inherently narrow band frequency sources. You only get broadband with a materials selection and some kind of tuning hack around those frequencies.

Potentially very clever as a way of getting more bandwidth up a fibre.

[Anonymous Coward]

"To create a white LED lamp, for example, today's technologies need multiple colour LEDs blended together"? No, just a blue LED with a yellow phosphor coating.

[Mike Shepherd]

Phosphor

You are right. That's how "white" LEDs work. (A device with several LEDs would be far more expensive).

[Mage]

need multiple colour LEDs

Worse, LEDs are nearly monochromatic. Putting R, G & B in a device lets you make a colour display with appearance of white, but rubbish for illumination due to the fact that really orange, yellow, cyan, magenta etc objects will be gray or wrong colour. Colour rendition is poor. A CFL or old style tube has a mix of phosphors to get a smoother spectrum. The better the colour rendition, the poorer the efficiency. Colour Temperature is NOT Colour Rendition.

LED lamps are poor colour rendition, but better than R G & B LEDs because the "yellow" phosphor is a broad spectrum. Often objects with reds and cyans are poor colour accuracy. As the phosphor ages, the light becomes more violet. They are ghastly compared to CFL or fluorescent tubes, which can be poor if higher efficiency types. Halogen is as good as artificial light gets, but of course the better colour temperature / higher efficiency ones are running hotter and have shorter life.

A "white" laser is only good for a projection display.

[Frank Bough]

Re: need multiple colour LEDs

Halogen incandescents are great but Xenon even better.

[Mage]

Re: need multiple colour LEDs

For efficiency or projector lamps. Not for room illumination:

Xenon, operated as a 'neon light,' consists of a collection of mostly spectral lines, missing much of the continuum radiation needed for good color rendering.

A flash tube is more incoherent and broader spectrum, closer to continuous white light. Far better than LED camera lamp.

https://en.wikipedia.org/wiki/Xenon_flash_lamp

High power Xenon Arc Lamps are not going to be used as room lighting

https://en.wikipedia.org/wiki/Xenon_arc_lamp

The spectrum of any Xenon lamp is inferior to a Halogen. It's hugely more efficient though.

[tony2heads]

Re: need multiple colour LEDs

I think it could make a good holographic projection system.

[Mage]

Re: need multiple colour LEDs

Yellow or Cyan can be:

a monochromatic source

OR

a mix of monochromatic sources

OR

a mix of broad spectrum sources.

Magentas are an illusion in sense they don't exist by splitting white light in a prism. They are a mix of colours from high frequency and low frequencies of the spectrum with the green our eye's green sensor uses depressed. Such objects will be unnatural if seen in discontinuous fake white light (e.g. Violet LED + yellow phosphor, or worse R G B LED even if colour temperature is correct).

Real life objects have broad spectrum of reflection or else they appear dim.

The R G & B of our eyes responses are very broad indeed and overlap.

Any discontinuous spectrum seriously distorts the perceived colours. Colour video is a trick. You use broad spectrum genuine white light to illuminate and then the camera sensors must NOT be narrow R G B filters, but overall have the same response as a typical eye (thus red has tiny blue response and some green, and Blue has some green and very little red). Green sensor peaks at green but has some sensitivity on the entire spectrum.

Then the display can use monochromatic R G B at the eye peaks, or for less colour range, other sources with the data matrixed. You can even add pure Yellow and/or pure Cyan too as long as the driver matrix is correct. Monochromatic Cyan stimulates Green annd Blue part of eye (and a little red) and Mono Yellow the Red and Green plus a little blue). This might be done to make whites brighter or improve pastel shades if the R G and B are not the ideal frequencies.

See https://en.wikipedia.org/wiki/Colour_perception

also

https://en.wikipedia.org/wiki/File:Cone-fundamentals-with-srgb-spectrum.svg

Note the lens and covering of the eye blocks almost all UV. Everyone is more UV sensitive in the blue if a synthetic lens with no UV filter is fitted. Some women do appear to be slightly tetrachromatic, so they will not be so impressed by your new TV.

[Kernel]

RE: Sounds like a functionally graded material at the nanoscale.

"Potentially very clever as a way of getting more bandwidth up a fibre."

Not really - multiple wavelengths in a single fibre (using tuneable lasers) is ancient history now days.

The trick is not in getting the multiple wavelengths into a single fibre - that's comparatively simple simple and can be done with passive devices - the real trick is the electronics needed to encode and modulate the lasers then decode and error correct at the far end.

[A K Stiles]

White Lasers

Presumably these would need to be mounted on a Great White shark then?

[Dieter Haussmann]

The vast majority of white LEDs are blue through to UV LEDs that excite a phosphor coating. The whiter they are, the more exotic/expensive the phosphor recipe. Mixing other wavelengths looks horrible as the colour LEDs are usually emitting at narrow bands of wavelength.,

[Martin an gof]

Panasonic make "Laser" projectors

They have essentially two models in their "Solid Shine" range. One is actually two LEDs (red, blue) and a laser (blue with a green phosphor):

PT-RZ470

Being a DLP projector, having three "fast" light sources saves you from the dreaded colour wheel (rainbow effect) or from having to have three DLP chips (expensive, and the colour filters have a short lifespan).

The other seems to have a cluster of Lasers (no idea of the colour) shining on a single phosphor wheel which, I assume, produces a mixture of colours. This light is then sent through a "virtually segmented" colour wheel. No, I don't know what that means either.

PT-RZ670

We have a couple of the LED/Laser projectors where I work. We use them for 3D film showings where the fact that they are degrading slowly together is a benefit (traditional lamps get difficult to calibrate, especially if they are different ages). I'm looking at buying a few of the Laser-only projectors for a side-by-side application. They're a lot more expensive up front than their traditionally-lamped equivalent, but you do save about 10 lamp changes (2,000 hour lamps) over the lifespan.

Lasers in the house? Might work with phosphors, but I'm not a huge fan of LED domestic lighting yet, and don't get me started on those awful flickering LED tail lamps on cars!

M.

[Anonymous Coward]

Re: Panasonic make "Laser" projectors

I've changed to LED house lighting (not the whole house but most of it) and it's much better than the CFL lights they replaced.

The quality of light, subjectively, is excellent and there's no delay.

I experimented in one room and am now slowly changing all of the bulbs in the house.

I agree on the car thing,though.

[Martin an gof]

Re: Panasonic make "Laser" projectors

I've changed to LED house lighting (not the whole house but most of it) and it's much better than the CFL lights they replaced.

Of course, that's an opinion. I can only go by what I've experienced. CFL is a mature technology and - startup aside (most CFLs still take a half second to come on, and many still need a few seconds to "warm up") - I prefer CFLs, at least for "standard" fittings. LEDs work much better in the smaller fittings, undercupboard lighting, that sort of thing.

We have a heck of a lot of LED lighting at work and have replaced most CFLs, particularly in GU10-style fittings. What we have noticed is that the stated lifespan is nowhere near accurate. The LEDs themselves are fine, but the power supplies are awful and we get a lot of premature failures, very nearly all of which are due to dead power supplies. This is true of "consumer type" GU10 fittings as much as it is of "industrial" fittings costing perhaps a couple of hundred pounds.

M.

[Gartal]

Doncha lovit?

One of the real pleasures of reading Reg comments is finding stuff like this, where people with brains and an understanding of more than bacon get technical in their comments. Thank you ball boys.

(No sarcasm, genuinely pleased)