Looking for a specific compact fluorescent bulb? This is the Halco model PL13S/E/41. It's a 13-watt CFL that puts out a cool white light (4100K color temperature). It has a 4-pin base (usually a square base with 4 little pins), so it's not your standard screw-in bulb - it's meant for specific fixtures that have a matching socket. Brand new, unused, in original packaging (could be retail or simple packaging). Part number is 109138, UPC is 807154191383. These are often used in commercial lighting, under-cabinet lights, some desk lamps, or specialty fixtures. The 4100K light is a bright, neutral white - not too warm (yellow) and not too cold (blue). Good for task lighting where you want to see clearly. CFLs are more energy-efficient than old incandescents, and this 13W bulb likely replaces a much higher wattage incandescent. Before buying, check your fixture! The 4-pin base means it probably twists and locks into place, or pushes in. Some of these bulbs are also used in emergency lighting units. If your old one burned out and you've got the model number, this is an exact replacement. Not as common as LED these days, but many fixtures still use them. Halco is a solid lighting brand. Keep in mind CFLs contain a tiny amount of mercury, so recycle properly when it eventually burns out years from now.