Our kitchen fixture won't come on for 3 to 5 minutes when the temperature goes over 90°F (32.2°C) and 90% humidity. It flickers and only reaches 80% brightness after that. It will occasionally flicker in lower, but still warm temperatures. It is fine below 60°F (~15°C).

I have tried replacing the tubes using both standard and ES tubes.

We rarely get above 90°F (32.2°C) without going over 90% humidity so I can't tell if it is the heat or the humidity causing the issue.

  • Need more info: does it have magnetic ballast or electronic? What age is it? Since you are in USA I assume a 120 volt system.
    – Skaperen
    Aug 4, 2012 at 22:44
  • @Skaperen - How do I tell if it is a magnetic ballast or electronic? It is a 120 volt system. I don't know the age. The fixture was in when we bought the house. I did look for a year stamped or printed inside the fixture, but with no luck. Thanks
    – Mike Two
    Aug 5, 2012 at 11:34
  • Duplicate of diy.stackexchange.com/questions/48001/… ?
    – keshlam
    Aug 24, 2014 at 18:16

3 Answers 3


By the sound of things you must be using the older ballasts with a starter plug. These ballasts cause flickering of the bulb and this constant flickering causes damage to the ballast itself.

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The ballast has to generate a very high voltage to "spark" the tube. Once the tube is glowing the ballast can relax and give a constant power output. The state between changing from high output to regulated is very stressful for the components and the starter plug is also responsible for handling this change.

Tubes need to be replaced every 12-24 months because the gas inside the tube loses it health properties even though it still emits light. So technically it becomes bad for your eyes because it starts to produce unwanted UV light.

I would suggest removing the old light fitting and buying a new one and INSIST on an electronic ballast. The electronic ballast does not need any starter plugs and handles the initial output voltage much better. It does not cause flickering (but if there is a problem it just does not turn on). These ballasts MUST match the wattage of the tubes. Higher or lower wattage will result in shortened life of the tube or not turn on at all.

The electronic ballast will not be influenced by humidity or temperature that much. It just runs.

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The differences...

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  • If you have a polycarbonate diffuser under the bulb, even if the bulb starts to emit UV, the diffuser will block it; polycarbonate is opaque to UV. (I don't know if you're correct about emitting excessive UV after a year or two, though I doubt it.)
    – derobert
    Aug 9, 2012 at 19:33
  • That is interesting about the polycarbonate! Never knew about that. Some lights have clear warnings about increased UV radiation after a certain period of use.
    – WillyWonka
    Aug 14, 2012 at 12:25

Fluorescent bulbs use a hermetic seal, which means no humidity will penetrate the bulb itself. This seal is necessary to keep the toxic mercury vapor from leaking out into the environment.

Humidity can cause corrosion of the metal fixtures on the ends of a fluorescent bulb, impeding its ability to transmit electricity. The corrosion is easily avoidable by purchasing a weatherproof fluorescent bulb, as they are resistant to corrosion.

Excess buildup of condensation on the outside of the bulb can cause it to take longer to turn on. The temperature difference on the glass negatively affects the delicate process within. Wiping the condensation off the bulb and waiting for five minutes will remedy the problem in most situations. Additionally, purchasing a weatherproof fluorescent bulb will avoid the problem altogether.

  • Thank you for your answer. We have had cooler weather for a few days. I will try this as soon as it heats up again.
    – Mike Two
    Aug 8, 2012 at 10:44

Humidity alone can interrupt or delay a fluorescent bulb from 'starting'. This can happen with older canister capacitor starting 'cans' or solid-state ballasts. Humidity dampens or shorts the bulb. A strip of foil breaks the humid envelope on the bulb (prevents thin condensate coating or humidity).

Another method is to rub your dry hand or cloth along the length of the bulb. The static electricity (high voltage/low amperage) is often enough to 'start' the bulb.

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