ALZO 27W Joyous Light Full Spectrum CFL Light Bulb 5500K, 1300 Lumens, 120V, Pack of 4, Daylight White Light Natural daylight balanced color temperature of 5500K with 1300 Lumens output and CRI of 91; great for reading, for various tasks that require visual accuracy and also as a plant grow light; pack of 4 This is a large bulb that might not fit standard household lamps, see diagram above; Dimensions: length: 6.5 inches; width (diameter): 2.5 inches; width (diameter) of socket: 1 inch.; fits all medium-base E27/E26 sockets Generates very little heat; all ALZO Joyous light bulbs are flicker-free Energy saving, uses about 1/4 of the energy of a comparable Tungsten bulb, with about 10,000 hours bulb life Important: ALZO CFL bulb life is based on the bulb in an open air fixture with sufficient ventilation; when ALZO bulbs are installed in fixtures that lack adequate ventilation, the life of the bulb will be greatly reduced.