Using refraction and rainbow technology, it should be possible to advertise right on airborne drops of moisture. Simply vary the color makeup of your light source. For example, if I want to draw a curved rectangle, I'd shine full spectrum light to the right and left sides, and deep blue and violet everywhere else.
This would be eye-catching advertising with many uses. I'm imagining a campaign: "Free umbrellas to the next 100 customers at Ursula's Umbrella Emporium"-- Worldgineer, Jun 23 2006 Thanks for the inspiration, Charlie. Use_20of_20Rainbow_20Science [Worldgineer, Jun 23 2006] Water Screens http://www.lasersho...t/water-screen.html [theircompetitor, Jun 23 2006] Mist projections. http://www.art2arch...eventful/prague.htm [2 fries shy of a happy meal, Jun 24 2006] Moonbow http://en.wikipedia.org/wiki/Moonbow [Ling, Jun 25 2006] Yup, that sounds like Rainbow Pseudoscience.-- nihilo, Jun 23 2006 [ni] - how so? It's simple refraction, combined with filtered light.-- Worldgineer, Jun 23 2006 This reminds me of the Batman call for some reason...-- BJS, Jun 24 2006 It would be a lot like the Batsignal, but I don't think it would work well. The described technique is interesting, though.-- baconbrain, Jun 24 2006 Why wouldn't it work well? I'm picturing the resulting image looking quite a bit like a rainbow, only with pieces missing (such as the box in my example). Sure you'd need a lot of light in the daytime, but you could use this at night using less energy than a spotlight.-- Worldgineer, Jun 25 2006 I disagree. Let's compare it to a spotlight shining on a cloud. This works using diffuse light, shining in all directions. One way to estimate the energy used is by imagining all of the locations you could be in and see it. Right under the cloud you'll see a bright light above, and it will fade as you get further. But you'll still see the thing for miles.
In contrast let's look at the rainbow example. This would work using refraction, which is similar to reflection. Refracted light doesn't go everywhere like diffuse light - it stays fairly coherent. This hurts us in that not everyone within a few miles radius can see it, but helps in that since only a relatively small area will see it you can both target an exact location, and it will use less energy.
Of course, this changes with the density of the rain storm. Some light won't refract, but will instead pass through without hitting rain. If you have a very light mist, you may waste a lot of energy.-- Worldgineer, Jun 25 2006 Link-- Ling, Jun 25 2006 Good link, [Brau], but that technology uses diffusion, which is more like the spotlight-on-a-cloud phenomenon.-- Worldgineer, Jun 25 2006 Yes, good link.-- skinflaps, Jun 25 2006 Could someone in the know tell me why there is a little question mark in front of the title of the link that I added? Is it that far from the mark?-- 2 fries shy of a happy meal, Jun 27 2006 We're supposed to flag links that cannot be accessed. Yours seems ok, though. Just 'unflag' it.-- methinksnot, Jun 27 2006 Limited viewing angle: definately. But that could be a good thing. I can imagine positioning your projector such that it's visible from a freeway or other high-volume area.
Difficulty: The sun does an ok job just by throwing light everywhere. Yes, this would only work if rain is falling in a particular place, but then rain falls everywhere at some time.
(sorry [2-fries] I had flagged the link because it wasn't working - it's working now)-- Worldgineer, Jun 27 2006 Wouldn't the viewer need to be looking from behind the raindrops your shining on ?
I thought rainbows worked like Prisms (like the one of the cover of Dark Side of the Moon) - where light comes in one side and is bent slightly as it leaves the other side ?-- monojohnny, Jun 27 2006 But I guess you meant artificial raindrops here....
Like a fountain or something....-- monojohnny, Jun 27 2006 No, I mean real rain (though a fountain should work as well). And yes, you'd have to position the light source correctly (at a 42 degree angle above the observer's head, with the angle measured at the rain).-- Worldgineer, Jun 27 2006 Have a bun then ! [+]-- monojohnny, Jun 27 2006 random, halfbakery