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OK. Hidden camera, big deal right?
But, there's many ways to spot a hidden camera, as they all need line of sight. Those dark glass bulbs are obvious. In a featureless hallway, you can spot hidden cameras easy. And, they all need housing for the parts.
Here's the twist, you can hide the camera
inside a light bulb that's ON. In a flashlight, in a ceiling light, etc.
There are at least 2 different ways to do this:
1. Have the picture frame capture rate, to happen at collection intervals that are 180 degrees out of phase with the natural AC peaks of the power source for the light filament. (Current capture rates are certainly within 60 Hz for AC = 0.016 seconds exposure)
2. Have the camera filter out the light frequency signature of the bulb itself (to subtract the noise of reflected light within the bulb). This would allow for longer exposures.
In either case, the bulb can already be designed to take the nearly point-source of the filament and spread it to the space, so that same illuminated space would then re-focus the returned light (to capture as an image) near the same spot where the filament is. So, a minor off-center of the filament, with a small camera (mini CCD) just oppositely off-center should get a pretty good image quality.
||[Ian] - it is, in the sense of light interference, which is just addition of the waveforms. You don't notice any systematic interference pattern as in school "two slit" experiments because the light source is large, not coherent, and not single-frequency (you're not large and incoherent, Ian, just the light reflected off you).
Method 1 above wouldn't work, because the bulb filament continues glowing throughout the AC cycle, because it's hot.
||Firstly, lights don't ficker on and off in an ac current, they just get hot and glow. I think it should be possible to shade the camera from the light in some way though.
||It's handy that you have a ready power source, I believe you can also use power cables to transmit data by varying the amount of energy consumed and monitoring it elsewhere. I think LG do it with washing machines.
||OK/right about that filament being hot. Scratch #1 method then unless there are lights that really flicker... (Do fluorescents really flicker on/off at a constant rate?)
||I'm not sure that any sort of frequency
filter would work either. Since any
colors you (or the camera) see are
reflected light coming from the bulb
(assuming a single light source) any
attempt to filter out the light
frequencies would also filter out the
returning light from the object being
observed. This could be solved by
using either multiple light sources
(track lighting or such) with differing
frequencies, or a camera that picks up
an IR frequency that is not generated by
the bulb, but is generated by the object
being observed (body heat). But neither
of these would produce clear normal
||Frequency shouldn't be too hard to filter on. After all, you know the signature of frequencies from the bulb, and can subtract those out.
||What you're shining the light on may not be dark already, so the reflected light would be enough from other sources to pickup on.