UV 253.7nm, GERMICIDAL lamp: 3 watt, 63 mm x 20 mm Dia, ushio, Screw e17, 17 mm across threads, Clear Glass tube, This bulb is made by USHIO, GTL3 GERMICIDAL BULB E17 BASE - 3 Watt Clear Germicidal Lamp Intermediate (E17) Base 10.5 Volt .30 Amp 2.48" Maximum Overall Length, 3,000 Average Rated Hours. Spectral UV 253.7NM. In these bulbs, an arc forms across the ends of the filament. These bulbs need a current-limited special capacitor / ballast (or high resistance) power supply that delivers about .33 to .4 amp to the bulb with about 10.5-12 volts across the bulb. Do not connect these bulbs to voltage-regulated power supplies; either little/no arc will form or the arc will "blow up" and melt one or both ends of the filament. The light emitted by these lamps is harmful to both skin and eyes and must only be used in enclosed fittings that prevent the light from escaping. Installations with these lamps are to be screened off completely.