Why Go Dark
Going dark, works on the fact that there’s less noise, less traffic and less people outside making sounds that could potentially contaminate your investigation data. By removing as much outside contamination your effectively attempting to control the audio aspect of the investigation. It's also a matter on convenience, many people work during the day and so evenings are the only available time to conduct an investigation. Another is the belief that spirits draw upon energy to manifest, so during the day the spirits can simply draw off the natural energies from the sun BUT by removing the sun (not literally) and limiting the power being used your essentially forcing the manifestation to draw upon your own energies or that of your equipment. A phenomenon known as battery drain, though battery drain is yet to be a proven factor of an investigation again it remains an inconclusive theory.
Control is such an important part of an investigation that you really have so little anything you believe you can control is a must, from noises outside to whose where and when in the location being investigated. Being able to identify the different light sources makes analyzing evidence easier. So by ‘going dark’ you are controlling the various different sources of light from that of a flashlight, IR illumination to the LCD screen of a camcorder. This also comes back to the idea of less traffic, so by going dark your heightening your senses, your attempting to control not only the energies that a spirit or ghost can use to manifest but also the light sources making evidence review easier and potentially eliminating false positives.