I hope this doesn't sound too odd :) what i would like to achieve is a proximity sensor using arduino which will sense the distance between a led grow light and the top of some plants (canopy) I would like to have two motors that move the led light up and down automatically, keeping the perfect distance from top of plants to the led grow light, i'm not sure the best way of achieving, any ideas and help would be greatly appreciated many thanks :)
I would have thought that one stepping motor would do to move it. The sensor could b tricky depending on what sort of distance you want. IR sensors work well only over a limited range.
See attached artistry for how you could do this with one (or a few) light-dependent resistors / phototransistors. The idea is that, when the light is too high, the sensor will not be shaded. Or putting that another way you would gradually lower the light until the sensor becomes shaded, or vice versa.
You could probably also hang the light sensor directly below the light so it pokes down through the canopy of the plants. A straight rod shouldn’t cause much of any plant damage.