The Arcadia Reptile Halogen Flood lamps are powerful, crisp, bright and Infra-Red-A rich. They are very energy efficient being better reflected and insulated than standard glass lamps. This enables them to provide high levels of heat and visible light. The Arcadia Reptile Halogen Flood lamp has a built in metal reflector for optimal light delivery to the basking zone. All Arcadia Halogen Lamps are dimmable making them suitable for use with a dimming thermostat for optimum safety and temperature control.Arcadia Reptile wide beam Halogen Flood Lamps are powerful and robust and should be used with a suitable dimming thermostat. Sizing: 35w - PAR20 - 2.5in / 6.35cm* Diameter 50w - PAR20 - 2.5in / 6.35cm* Diameter 75w - PAR30 - 3.75in / 9.5cm* Diameter 100w - PAR38 - 4.75in/ 12cm* Diameter *approximate due to rounding in conversion. PAR1 = 1/8th of 1 inch / PAR20 = 20/8ths of 1 inch.