While researching a new project (as us mad-scientists-types are prone to do), I found this amazing video. It’s basically a clear chemical that undergoes a reaction in the presence of UV light that makes it very quickly turn green. But, the key here is that the reaction is also quickly reversible – in about a half second after the light is removed, the liquid reverts back to the clear state.


This reminds me of a fictional Dr. Seuss invention, the “flash-dark” (from “The Cat’s Quizzer“), that’s like a flashlight except it shines a beam of darkness instead of a beam of light.

Practical uses? I can imagine this being used with large video projectors.

Traditional projectors are neat because it’s easy to make large images – just use a large screen. A major drawback, though, is that the darkest color that they can produce is the color of the screen — and that screen is usually white to reflect the most light. As a result, projectors must be used in low-light situations, or with exceedingly bright bulbs.

Reflective LCD displays (like the kind found in watches, not TVs) work differently – instead of creating light, they just block out the ambient light in areas to create dark spots – as a result, they are low-power and work great in bright light. But, LCD displays don’t scale up to large sizes easily because they can’t be projected.

I think that you could get the benefits of both of these technologies by painting this chemical on a wall. An ultraviolet projector would project an inverse image, creating a large dark green image that is visible even in bright light. There are two main drawbacks, though, that would probably limit the use of this technique to informational and artistic displays: First, the very slow response time (600 msec, which is slower than eink) prevents it from displaying full motion video. Second, it’s only one color – turning it in to a full-color display will require a lot more work.

So, what would you do with something like this?

More information:

  • pineappleclock.myopenid.com

    Depending on the permeablity of the substance to UV, you could fill a cylinder with this substance and vertically scan it with a UV laser, then project a synchronized image from underneath. If the horizontal scanline response time could be improved you would see a 3D image

  • Stephen

    I think you’re right to see this as a projector tool but personally I think this would be best seen as a projector screen, not the projector itself.

    You project UV light from the projector to excite the screen and turn the dark areas black and suddenly you have a projector that can do blacks. I don’t honestly understand it as a projector element but I’ll see if thinking about it more helps.

  • ehrichweiss

    The last I recall reading, there are no UV lasers in the hands of the public. There are/were only two methods of producing UV laser light; one involved exploding a nuke and the other involved some huge lab/warehouse in the U.K., IIRC.

    Maybe this is IR instead? I can’t see how anyone would be able to see if it were otherwise.

  • John Maushammer

    Stephen – yep, that’s the idea I was going for, but I didn’t explain it clearly enough :-)

    Ehrich – There has been a lot of progress in UV diodes in the last few years, but unfortunately it’s still at the experimental and pricey “lab equipment” stage. We had one at our company 2 years ago – it cost $30,000, was finicky, and died an early death. I’m sure things have improved since then.

  • Anonymous

    Fluorescence ?

  • Silverman

    UV lasers are not that advanced. CO2 lasers are UV, for instance, and they are commercially available. Even the homemade “air laser”, actually a nitrogen laser, emits UV.

  • Anonymous

    John, I too think this could be used in projection to create richer dark tones. Here’s two ways one could implement this on a small scale experiment. Both involve the screen coated with the chemical.

    Experiment 1 use two synchronized projectors.
    Projector A uses a non UV light source.
    Projector B is modified with an UV light source.
    [And negative footage?]
    Both A and B overlap on the projection screen.

    Experiment 2 a modified projector with both light sources quickly alternating. Each frame of footage should have an alternate light source. In effect the visible light would fill the “void” as the chemical clears.