R39 E17 Lava Lamp Replacement Bulb 25 Watt Reflector Type (2 Pack) Replacement Bulbs for Lava Lamps. R39 Watt Reflector type bulbs. 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.