Multiple-blower relative humidity controlled test chamber

An accelerated weathering apparatus includes a test chamber ( 30 ), a specimen supporting means ( 34 ), a light source ( 60 ) powered by a power source controlled by a ballast, at least one chamber air temperature sensor ( 26 ), a black panel temperature sensor ( 36 ), and a multiple blower system and control means ( 52 ). A first blower ( 12 ) draws and circulates outside or fresh air and as second blower ( 46 ) optionally draws recirculated air into an air mixing duct. The speeds of the fresh air and recirculated air blowers are independently regulated and controlled by a blower controller based on the chamber air temperature and black panel temperature, respectively. In addition, a humidifier ( 18 ) and humidity controller ( 20 ) regulates humidity within the system as required.