GTI Fluorescent Replacement Lamps 18in - F15T8/GL50F15T8 GL50 GTI T8 d50 Replacement Bulbs GTI GraphicLite 5000K lamps The precise spectral characteristics and lumen output are subject to an exhaustive quality control process to assure that each lamp provides true full spectrum, color balanced illumination and extremely accurate color rendition. The model number of the bulbs contain the size, wattage and type. For example: When looking at the model # F15T8 GL50. The first number 15 is equal to the