Manufacturer Bulb Type Pressure Type UV Spectrum
Aqua UltraViolet   Medium Pressure 185 - 400 nm
Emperor Aquatics T5, T5-HO Low Pressure 253.7 nm
WLim T5, T6 Low Pressure 253.7 nm

Definitions:
Bulb Type Rating

The "T" in this rating states the tube type, being Tubular, and the number represents the thickeness, being measured in 1/8th in. (e.g. T6 = Tubular, 6/8 in. diameter)

Pressure Type

Low pressure puts out a very narrow area, yet a high level of UV light at 254 nanometers. The medium pressure lamps don't put out a very high level of UV, yet they do produce a very broad range of UV over the entire spectrum that enables it to potentially kill more types of Microorganisms.

UV Spectrum

The UltraViolet light transmits a specific light spectrum that damages the Algae and possible protozoan's within the water.