Flickering or dead fluorescent light — tube or ballast?

What this error means

The documented diagnostic order: tube first. Look at the tube ends — heavy blackening means the tube is at end of life (light gray banding is normal aging). The definitive test is swapping in a known-good tube. If good tubes still won't light, the ballast is the suspect — supporting evidence is a worsening buzz, slow starting, or visible tar leakage from the fixture.

Symptoms

• Flicker, strobing, or half-brightness
• Blackened tube ends
• Tubes fine elsewhere but dead in this fixture (ballast)

Try this first (safe DIY steps)

1. Check tube ends for heavy blackening — that tube is done; replace (match length and type: T8, T12, T5)
2. Swap in a known-good tube — the most reliable single test
3. Twist tubes to reseat in their sockets (quarter-turn) — loose seating causes flicker
4. Good tubes + no light = ballast; that's electrician territory (or the LED-retrofit decision — see that guide)

Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.

When to call a technician

Ballast replacement is inside-the-fixture line-voltage work: ballast part ~$20–40, typical electrician visit ~$150 per fixture. Before paying that, read our LED retrofit guide — repeated ballast replacements usually lose to conversion.