I’m working with a small side-looking infrared emitter/receiver pair that I got from Sparkfun to see if I can detect blinks. My theory is that the surfaces of my cornea and of my eyelid will reflect (detectably) different amounts of IR light, thus allowing me to sense blinks. I’m getting awesome values from the pair using a 10k resistor, 25-1000, so almost the full possible range.
There’s not much reliable research online about the effects of long-term IR exposure. Some people say that because it doesn’t cause the iris to contract as bright visible light does, it will blind you if you look at it too long. Other people say that’s nonsense, claiming that the IR light in question would have to be much brighter than an LED to cause any damage. Still others (my favorite group) post frantically to medical forums after having spent hours staring at their remote controls while pushing the buttons (?!), suddenly panicked that they may have caused themselves irreparable damage.
I tested various brightnesses using a digital camera and varied resistance, and am using a highly directional light that will be aimed at the side of my cornea rather than directly at my retina, so I’m not too worried.
To detect reflection, the emitter and receiver need to be installed completely flush to the same surface and about 10mm apart. I get good readings when holding them up to my eye, a variation of between 50 and a 100, good enough to work with.
One hour later…
Mounted on the glasses, it doesn’t really work. There’s too much infrared variation in ambient light. I may need to use a camera. And my eye feels like I’ve been staring into the sun for too long. It might be fine to stare at an IR LED from a distance, but right up against your eye, it starts to feel not so good after very little time. I am nixing this particular plan.