Set of 2 R39 E17 Replacement Light Bulb Motion Lamp 30 Watt Reflector Type Set of 2 Replacement Bulbs for any of our Lava Lamps R39 30 Watt Reflector type bulb. Approximate Measurements: 2.25"L x 1.5"W(Top of Bulb) Base Measures Approximately 1/2" Specially designed to reflect and direct the light into the base of lava lamps in order to create enough heat to start the lava motion.