Underside of Immature Bed Bug
Bed bugs are cryptic. They hide during daylight and venture at night to feed. This is adaptive because their human hosts are typically sleeping when a room is dark. Moving bed bugs are more likely to be detected in the light. In laboratory tests*, bed bugs move minimally in light conditions. Within a short period after the lights go out, bed bug activity rises to a peak, then tapers off toward the time when lights go on.
Under continuous light, bed bugs maintain…
Source: Living With Insects Blog