Ballast (Lighting)

The Full Picture

A discharge lamp, such as a fluorescent tube or a high-intensity discharge lamp, needs help to start and cannot be connected straight to the line, because its current would keep rising. The ballast supplies the starting voltage and limits the running current. Older fixtures use magnetic ballasts, and later fixtures use electronic ones. LED fixtures use a driver instead, which does the equivalent job for a different light source. In construction the word also means crushed stone on rail track and the stone or pavers that hold down some roofing, so context matters when searching.

In new construction, the ballast is part of the fixture and is rarely counted on its own, since it comes inside the luminaire priced from the lighting schedule. It matters in retrofit and maintenance takeoffs, where the question is what stays and what is replaced. An LED retrofit of an existing fluorescent fixture may remove or bypass the ballast, or reuse it depending on the lamp type, and so the plan and spec must say which approach is used. Dimming is related: automatic daylight dimming adjusts the output of a dimming ballast, so a dimming control on a fluorescent system implies a dimming ballast in the fixture.

The drawings that define the quantity are the lighting plan, the fixture schedule and, on retrofit jobs, an existing-conditions or demolition plan. The schedule gives the fixture type, lamp count and sometimes the ballast type. The estimator counts fixtures by type from the plans, then derives the number of ballasts from the lamps per ballast, and the count is carried as EA with the lamp count and ballast type as the description. Disposal of removed ballasts is also scope worth reading in the specification, because old equipment may be handled under special disposal requirements.

Common pricing mistakes are counting ballasts from the fixture count without checking how many ballasts each fixture type holds, assuming every old fixture needs a new ballast when the spec removes it, and missing the extra labor to access fixtures above ceilings or in high bays. Because LED conversion has changed what the schedule asks for, an estimator should read the whole retrofit scope before assuming any ballast quantity.