Displays That Harvest Light Instead Of Creating It

mach10 writes: "An article here shows that a scientist has been able to create fibers that collect ambient light, strong enough to power a dotted matrix for display. It can reach 30 times ambient light, and they are soon hoping to expand the area to replace signs on roads. Hrm ... But my sundial watch still doesn't work in the dark =\" Add this to some ultra-efficient light source (like white LEDs?), a low-power processor, human power and some solar cells, and most of my requirements for portable computing happiness would be met.

Comments

Re:Cheap night vision?

[Matt_Bennett]

So, when (and where) can I pick up my almost free night vision goggles?

They're already here (kinda). Binoculars (with large lenses) collect more light than the unaided human eye and can serve to amplify the light- you just need to find binoculars that have large lenses and low magnification. This works especially well in low light (dusk, not dark) situations.

Only need a few cm, works under any light level

[The Fun Guy]

My physics-major college roommate used fluorescing glass fibers in a project at Fermilab, and he brought some back home to play with. They were maybe 25cm (~10 inches) long, and very narrow, similar to fishing line. When exposed to light perpendicular to its length, a surprisingly bright purple light came out of both ends; the brighter the incident light, the brighter the flashlight-type dot of light that came out of the end. If you covered up part of the fiber, light still came out the end, just dimmer. The longer the fiber exposed to the light, the brighter the dot. We tried this with incandecent and fluorescent bulbs, bright sunlight, dim sunlight, candlelight, flashlights of various brightness, any light source we could lay our hands on. The only thing that changed was the intensity of the glowing dot.

A similar technique is used in light-gathering spotting sights. These are popular with bowhunters, and are essentially a rod of fluorescing plastic (~5cm long, ~0.5cm in diam) that you mount on your bow to help you sight on the target. The end is tapered and set at a right angle such that the incident light that hits the side of the rod makes the tapered little point (~0.2cm in diam) glow really brightly. Based on my rough estimates of the dimensions, I'd say that the area of the side of the rod (capturing incident light) is ~100X the size of the glowing tip. As with the narrow fibers, it works under any light level except complete blackness, and remember, under very dim conditions, even a faintly glowing dot looks bright.

Human power, solar and collection systems

[mr]

A well conditioned human can pedal at about 45 watts for 2-3 hours, 30 for a long time, and 60 for 30 minute bursts.

So, the human powered option is out for many applications.

The fibers *MAY* have applications in solar systems. What kills the cells is heat buildup more than anything else, and the concentrator *MIGHT* not allow infra-red to pass, but allow the other parts of the bandwidth to pass.
A company called (methinks) marathon solor used to have a light conentration system for its cells to boost output. Such a method is economical *IF* the cells are expensive and the fiber is cheap. (oh, and they are now bankrupt)

Given that you can now buy solar cells as shingles to go on your roof, I have to question if the economics are right to use fiber concentration on silicon cells.

Home power is a nice place for figuring out how to get off the grid, and this gent thinks the future for cheap solar is heliostats. Combine a heliostat with a helium-as-working-fluid sterling cycle prime mover, and you may just have a winner!

Always the right brightness

[ESD]

This is very interesting: because the fibers collect ambient light, the screens will get brighter if there is more ambient light. This is very useful if you are sitting in an environment where the light-intensity changes a lot (for example: sitting in a train in bright sunlight, and then the train goes into a tunnel)

This would solve a lot of my problems with my TFT-screen.

Re:White LED efficiency that of parent LED

[kobotronic]

The super-highbright white LEDs from Nichia uses a blue LED for the base light, with a coating of yellow phosphor at the base that responds to the ultra violet wavelengths to create a somewhat cold-looking but highly power efficient white light. Like the other guy said, the resulting light spectrum is spotty, there's big peaks on blue and yellow and very little else. The light is great for utility light and display backlight, but it's somewhat antiseptic and unpleasant for room illumination. Like an old-type fluorescent tube. I fit ten of these in the hood of my car, for light at night in the event of an engine failure. And they use virtually no power at all.

Interestingly, the blue Nichias has quite a lot of UV output, which can be used for blacklight applications with a filter.

Unfiltered CCD cameras hate the blue Nichia light, probably because of the UV stuff. They think the (rather pretty) deep blue light is tinted magenta or cyan.

3000% energy efficiency

[kyz]

"So, if these fibres take in light and output it 30x brighter, why not make a feedback loop?"

It's a great idea, but the problem is that you're getting more energy out of the system than you put in. Energy efficiency doesn't go over 100%, so either these phosphors have energy hidden in them (and they'll run out over time, like batteries), or this system collects a lot of ambient light and concentrates it into a small space.

Re:3000% energy efficiency

[malahoo]

No, it works like this:

1. Lots of free, ambient light hits the fiber
2. Some of the energy in this light causes the fiber to flouresce
3. The light produced by this flourescence is channeled to and focused on the ends of the fiber.

You're not violating Thermo, because the input energy is not amplified by 30x, it is being transduced, with considerable inefficency, and sharply focused.


If you're not wasted, the day is.

I can't help it,

[FreeJack1]

but after reading the article and especially observing the image alongside it, I have to say that I'm impressed that the scientists have finally discovered a Lite-Brite toy! What is it that they're hoping to accomplish with it, besides drawing pretty and colorful pictures?
Never mind...
--

Vote Homer Simpson for President!

Obvious problem

[malahoo]

Not surprisingly, the article is pretty thin on details, and since my extensive 3-minute Google search yeilded only inaccesible servers, I'm still wondering: how much surface area do these things need to collect light? From the article:

When ambient light hits a fibre, the dye molecules fluoresce, producing light of a particular colour, which is reflected towards the ends of the fibre.

But it doesn't say how long each fibre needs to be to produce its two dots of light. I assume that (up to a point) as you increase the lenght of the fibre, the ends get brighter. So for 30x ambient do you need a 1 meter fibre? 5 meters? 100 meters?

Let's see if we can find some real linkage...


If you're not wasted, the day is.

Not a power source

[KarmaBlackballed]

...Add this to some ultra-efficient light source...
Some folks are misunderstanding the principle here. These fibers are collecting ambient light, not amplifying it. Like all things in the physical world, there is a power loss through the fiber, so you are not getting something for nothing.

Think of this invention as analogous to a rain gutter where light is the water and the gutter is the optical fiber. When it rains, water is "collected" along the length of plumbing that edges the roof. No extra water is created, but the volume of water at the end of the pipe is an amplification of what would have been there without the gutters.

The innovation here is that no one has created a fiber that easily collected ambient light along its length before. The only other way I know of to focus ambient light is to use mirrors or lenses. Clearly the fiber sounds cheaper, less bulky, and less fragile.