this exact question was explained to me by a genius friend, and a grower ... 'Custom39' :thumbsup: ... the short answer: place the LONG side of the lamp/reflector towards the SHORT sides of the cabinet ... I know that sounds the opposite of what you'd first assume, but realize, a minimum of light is projected from the ends of the lamp, more from the sides of the lamp/reflector ... thus, more light is reflected towards the distant ends of the cabinet ... :jointsmile: (by the way, my cabinet had it the 'wrong' way, because I had no choice, limited space) :jointsmile: