Light sensors (can also be photo sensors or a photocell) are fairly simple, and semi-cheap. You can look at all the normal electronics websites to find some. For example Sparkfun had these:
Both are fairly easy to understand. I don't think you would need a sensor for each individual blind piece though, just one sensor for an entire column maybe. Really, that's up to you, since it's your design, but why spend the extra money on extra sensors if it's really not needed. Blinds will generally have the same brightness on them at the top as at the bottom.
As far as the sensors being inside, either of those would work. I don't really understand the idea a ton except it's effectively filling a "bag" with air, and then sucking it out. XD I'd do the more simple approach of having a stepper motor turn regular blinds up or down based on daylight, but that's me, simple in nature.
O-o I feel like I'm rambling. Anyway, Pretty much all photo/light sensors work in a similar way. They either give or take resistance based on the amount of light they have. If it's lower then a certain amount then it would be triggered as off, and above that certain point would be on.
XD I feel like my post was kind of rambly and pointless... but, the point is, that's what they are, and a place you can get them, and a brief (and probably horrible) explanation of how they work. Sorry if it was a horrible post. (brain isn't working well today...)