Electronic – repeatedly turning an incandescent light bulb on and off every 20 seconds will cause damage to the bulb

energylightrelay

I have seen similar questions to this one but none of them were asked in the range of seconds only minutes.

I just finished building a incubator for chicken eggs and I am using an incandescent light bulb as source of heat. The thing is I used a pretty sensible digital termometer an the light bulb turns on, last ~20 seconds on and then turns off again.
I'm worried this will cause any damage to the light bulb or the relay that acts as a switch.

The incubator works well but I dont want to replace parts every week.

Best Answer

I'm not sure this is so mich an "original" answer as a combination/explanation/redinement of the other 2 already posted answers, but I'll try to help a bit.

  1. As transistor pointed out in the question comments, the 'bulb'-life impact of rapid switching on several varieties of lights is discussed in some detail in If I flick the light switch on and off will it damage the light?

  2. Autistic, Rothloup, and 2 posters in the other thread are all right about 'dimming' the incandescent greatly improving bulb life.

    • I would recommend using an inductor in SMPS buck-converter arrangement as likely being the most efficient (be careful though, the efficiency of that one inductor could surprise you, incandescents have a very non-linear response & tend to respond well to under-voltage drive).
    • While the buck converter could arguably be run on from non-rectified ac current, I would personally recommend using rectified & conditioned/smoothed DC (for predictable performance), and a pwm management that never cycles slower that 40KHz (so you don't have to hear it 'sing').

  3. You should definitely replace the relay with solid-state components.

    • At the least, a triac or optoisolator/'solid state relay' can switch your load faster than a mec. relay & love longer.
    • Better by far would be using a bridge rectifier & a capacitor to convert your input to smoothed/conditioned DC, then use a power MOSFET (if you get a 'logic-level drive' one, it won't even need any external buffering transistors) to run the aforementioned buck converter.

  4. Putting it all together, if you PWM a buck converter, with solid-state switchgear, to keep the light somewhere between 'just warm' and 'hot, but barely glowing,' you should be able to maximize your energy efficiency, component lifetime, and the precision/stability of your incubator's temperature control.

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