Re: What is the easiest way to change light intensity?

A simple method would be to use an AC light bulb and a lamp dimmer. Try an "inline" lamp dimmer available from the larger hardware stores. However, the color of the light will change (it becomes yellow or orange at the low settings.) Choose a light bulb which is only bright enough for your purposes (don't use a 100-watt bulb if you're never going to need that much light.)

Another method would be to put a low-wattage frosted light bulb in a box and make a simple sliding shutter. Open the shutter a tiny crack for dim light, or open it wide for bright light. The bulb should be frosted, otherwise the shutter will make a light beam which changes size, rather than a light beam which changes brightness. Hint for design: the shutter could be a triangular hole with a flat piece which slides across it. That way the hole would always have a triangular shape, even if it was mostly covered by the flat piece. WARNING: if you seal up a light bulb inside a box, it can heat up and become a fire hazard. Use a low-wattage light bulb or some sort of fluorescent tube, and provide plenty of cross-ventilation.

Do wood lice care about the changing SIZE of the light source? Maybe. If you place a piece of wax paper somewhere between the wood lice and your light shutter, then they will see the changing brightness, but they won't see the hole which changes size.