22-gauge steel, no passage of air through the fixture and into the Cleanroom ceiling. Low brightness acrylic prismatic lens supported on four sides in a flush metal door frame. Invisible hinges and slide latches. Gasketed door frames and lens available as option. Two or four rapid start lamps. Electrical components U.L. approved. Ballasts class "P", CBNETL. Available in 120 and 277V-60 HZ.. IBEW, AFL. White baked enamel.