Replacement light bulb.
Bright, full spectrum or "sunlight" color output (∼5000 K)
Note that at 1-1/2" diameter, this bulb is the equivalent of a T12 (12/8") or T38 (38 mm) fluorescent bulb.
In fluorescent tubes, for a given diameter, length correlates with watts. The longer the tube, the more Watts, and the more light output.
Fluorescent tube dimensions provided can be nominal, and may vary slightly within standardized min/max specifications.