Powered by batteries or electricity, these traps will attract adult mosquitoes when they are placed away from any competing light source.  Then the mosquitoes fly to the light, a fan blows them through a funnel into a jar or mesh bag that is suspended below the trap.  Traps should be turned on before it gets dark and turned off at daylight.  Humidity, temperature, wind speed, and direction might influence the number of mosquitoes you are able to trap in a night.