A magnetic ballast, operating from an AC source, produces an inherent sound
commonly referred to as "hum." Depending on the type of ballast involved, the
degree of hum varies. To aid in the selection of ballasts, most manufacturers give their ballasts a sound rating that generally ranges
from A to F. An "A" ballast has the least hum and is recommended for
relatively quiet areas.
Of course, sound rating of the ballast is only one factor in controlling noise. Other considerations must include the construction of the fixture, the fittings and accessories, ballast mounting, and the number of fixtures in the installation. Fixtures should be properly mounted and each ballast should be solidly mounted in the fixture. Good ballast-to-fixture contact will not only reduce noise but also help to conduct normal operating heat away from the ballast.
