Full spectrum light bulb that imitates daylight, energy star compliant, long life of about 10,000 hours; *) low energy consumption, good for treating Seasonal Affective Disorder S.A.D., or for starting plant growth. This is a Compact Fluorescent Light (CFL) bulb. Fits all medium-base E27/E26 sockets, but this is a large bulb that might create a fit problem with standard lamp harps of household light fixtures; a larger lamp harp is needed, see ALZO 9" harp, ASIN B0035LTIZE. Dimensions: L: 6.5"; W (Diameter): 2 1/4"; Length socket base to top of ballast: 2 3/4"; W (diameter) of socket: 1". Also available as a 15W bulb, see ASIN B0089MIH8I. *) ALZO CFL bulb life is based on the bulb in an open air upright orientation. When ALZO bulbs are installed in fixtures that lack adequate ventilation, the life of the bulb will be reduced. If an ALZO CFL bulb is installed in an overhead recessed light fixture with the bulb glass below the base, the life of the bulb will be greatly reduced. ALZO warranty for all CFL bulbs is 30 days.