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LEDs for the Blind
boowax writes "Tired of being blinded by those annoying laser pointers that have found their way into all sorts of places for the convenience of corporate presenters? Looked too closely at the underside of your optical mouse? Are you just dumb enough to look directly into a laser? Well, fret no more, for here is a new technique for stimulating and healing those damaged retinal cells using LEDs. Its also being tested for use in treating similar problems caused by mucositis (a side effect of chemotherapy) and other eye related maladies."
Laser diodes used in CD drives and whatnot are similar in principle, but the construction is somewhat different.
Here's the construction of one by Sharp, and an explanation of how they work.
Ali
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All the optical mice I've seen don't use lasers. If they did, they'd be required by law to have the standard laser warning sticker in plain view on them. I have yet to see a mouse with such a sticker.
They just use very bright LEDs. If you think about it, that's all that's really necessary. It just needs to illuminate the surface under the mouse with a color that the sensor is sensitive to.
The light from a regular LED looks nothing like that from a Laser Diode. Even the cheapest laser pointer has wonderful "scintillation", where the lighted area appears to sparkle.
This is caused by head and eye motion changing the light pathlength and interference patterns. It gives laser light a unique sparkle and shimmer that ordinary LEDs can only aspire to.
So the LED on the optical mouse is clearly not a laser, just ordinary light for lighting up the mousepad. And the cheapest $2.99 laser pointer really is a laser.
the mouse detects optical surface defects ("noise"), and determines some sort of rate of noise change and direction to figure out where you're moving the mouse. Which is why they don't work on very smooth surfaces, like glass table or desktops.
I always thought it was just a regular LED. Do optical mice like my Cordless Mouseman have actual lasers? The light spreads so much it does not definitely look like a laser, but i know nothing about hardware, so could anyone enlighten me on this?
Well, like the filament of the rectifier tube in my 1939 Stewart-Warner radio, it hurts my eyes to stare into it, and it's red, but it's definitely not a laser.
Lasers come in wavelengths (colors) ranging from invisible to invisible, and everything in between. For a variety of reasons, almost all the lasers you're likely to encounter will be red or IR (invisible).
You can tell a laser from any other source of light very easily:
Is the light coherent? As in, if you shine the light at the house across the street, does the dot appear to be the same diameter as it was when you pointed it at your hand? Coherency is a basic feature of laser light; some spread is normal, but if it spreads like a flashlight, it's not coherent.
Speckle. Laser light almost always appears speckled. Regular light consists of an infinite number of wavelengths of light mixed to make white. Ranges can be filtered out with sheets of glass, plastic, etc - think of sunlight in a stained glass window, there may be 300 different wavelengths that we would describe as red light. But laser light is at a peak wavelength, with some slight impurities. But it's very precise. If all your light is at one wavelength, when it hits an imperfect (ie. any) surface, some light will reflect back 180 degrees out of phase and cancel itself out (like adding -1 and +1, they cancel to zero). This accentuates imperfections on the reflecting surface in the form of speckle.
I don't see either one of these behaviors with the light from my own Mouseman. So, all I can assume is that it's merely a bright LED.
LEDs are certainly bright enough: many cars use LED third brake lights, some new Cadillacs and Mercedes are using them as the main taillights, and I've seen traffic lights in Toronto (Eglinton East at Sloan) and Ottawa (Gladstone at some intersection between Preston and Bronson), so LEDs are certainly up to the task of lighting an image of my mousepad.
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