NetBotz strongly recommends that you use day/night cameras to monitor low-light environments instead of adding unsupported parts to NetBotz appliances.
However, it is possible to add an USB-compliant light to USB port(s) of a 420/500 model as long as the light does not draw more than 500mA.
NetBotz Development Team also suggests that if you do add a light, place it away from the camera if possible, like in the other corner of the room, to avoid camera bloom.
Another ungraceful, unsupported option is to remove the IR filter from behind the lens, and replace it with a clear filter, add an external IR illuminator box to the room. The drawback to this, is that it is a night only solution, so in the day, the image will look bad.
Please note that all the above options are do-able but are NOT supported by NetBotz