To attain a state of night time darkness, the light intensity should be less than 0.4 lux (0.04 fc). During
darkness, care should be taken to avoid light seepage through air inlets, fan housings and door frames.
Regular tests should be conducted to check the effectiveness of light proofing. One way to do this is to
stand in the center of the house and turn the lights off. It will then be possible to see any light leakage into
the house.