Before entering into a discussion as to why digital ballasts are superior to the old-fashioned magnetic core and coil types, it may be helpful to know exactly what a ballast system is in terms of hydroponic gardening and grow lights.

All standard grow lights used in hydroponic gardening - whether some type of metal vapor or fluorescent - employ a ballast system. This consists of a housing, within which is contained electronic components that in essence "prime the pump." A fluorescent light has its own built-in ballast system; this builds up the energy required to activate the molecules inside the fluorescent tube, which in turn causes them to glow, emitting light. Metal Halide and HPS grow lights have "remote ballasts" which are housed inside a metal container. The components are what make up these lamps' main power supply. Together, they function as a "pre-heater," which allows electrical power to build up to the point that the lamp will run.

The drawback of these kinds of ballasts is that they build up the energy required to run the lamp, then sends it on all at once. The cold bulb is literally "slammed" with energy at full force. A good metaphor is the case of someone who puts a car in gear, disengages the clutch, revs the engine up to 4000 RPM then "pops" the clutch. "Pealing out" may be fun and impressive to onlookers (though illegal in most places), but as any automotive technician will tell you, can shorten the car's engine and drive train considerably.

It is the same with standard ballasts; the sudden surge of electricity tends to shorten bulb life. In addition, standard coil-type ballasts cause the bulb to "strobe," or flicker.

Digital ballasts eliminate this wear and tear on the bulb by providing a flow of electricity that starts out at a low level, then increases energy flow as the bulb warms up and achieves full brightness. Studies have shown that MH and LPS grow lights used with a digital ballast lost only 20 to 25% of their PAR luminescence (the wavelengths actually used by the plant) after one year; those used with a standard ballast had lost over twice at much over the same period.

It should be noted that digital ballasts vary in terms of quality and reliability. In general, products made in Chinese factories tend to be of inferior quality, and should be avoided. The best digital ballasts will run all types of grow lights, and be able to recognize the difference between metal halide, HPS or LED. If a bulb is defective, damaged or incompatible, or if a short circuit is detected a well-manufactured, U.S.- made digital ballast will automatically shutdown before a safety hazard is created.