Sags & Swells Symptoms - Lighting

Most lighting systems are tolerant of sags and swells. Incandescent systems will simply burn brighter or dimmer. Overall life expectancy may be affected, and the change in brightness may be annoying, but no other adverse reactions usually occur. This change in brightness is often called "flicker."

Fluorescent systems may not fare quite as well. Standard ballasts are typically more tolerant than are electronic ballasts. In both cases there may be some flicker, but the real concerns are with restarts and reliability.

If sags are deep enough, then the ballast will no longer be able to provide the energy needed to generate the arc inside the fluorescent tube. This means a dark lamp. If swells are extreme, then the ballast is stressed, causing premature failure.

High intensity discharge, or HID lighting such as mercury vapor, metal halide, and high and low pressure sodium lights are also more sensitive to sags and swells. While their response is very similar to electronic fluorescent ballasts, the lamps themselves are typically more sensitive than the ballasts.

A common problem is HID systems turning off during a sag. Unlike fluorescent systems that will quickly turn back on, the HID system must wait several minutes before being restarted. This is not only annoying but can be dangerous.