73375t filter when the illumination is provided by 40 to ¡50 Watt household incandescent bulbs, and the transparencies are to show the subject in its original colors (e.g., technical interior, architectural photographs, or reproductions). It should not, however, be used for moody interior pictures because unlike the KB ¡5 and KB ¡2 filters, the KB 20 filter corrects the light to a neutral balance, eliminating the warmth that we might intuitively expect from bulbs. Its filter factor is approximately 2.7.