In flood lamps used for photographic lighting, the tradeoff is made in the other direction. Compared to general-service bulbs, for the same power, these bulbs produce far more light, and (more importantly) light at a higher color temperature, at the expense of greatly reduced life (which may be as short as two hours for a type P1 lamp). The upper temperature limit for the filament is the melting point of the metal. Tungsten is the metal with the highest melting point, 3,695 K (6,191 °F). A 50-hour-life projection bulb, for instance, is designed to operate only 50 °C (122 °F) below that melting point. Such a lamp may achieve up to 22 lumens per watt, compared with 17.5 for a 750-hour general service lamp. COUNT 4
QSN1 At what temperature does a typical 50-hour-life projection bulb operate? ANS1 50 °C (122 °F) QSN2 Which metal has the highest melting point? ANS2 Tungsten QSN3 What is the typical life of a P1 lamp? ANS3 as short as two hours QSN4 How does the color temperature differ for photographic lighting? ANS4 higher color temperature