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Softlight

Save lightbulbs by increasing the warm-up time
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By fitting a capacitor to light switches, lights can be turned on or off over a short period of time (say 250ms). This will reduce the shock endured by the filament extending the life of the light bulb. An additional benefit would be the aesthetic effect of having the light turned on or off slowly.
andyg2, Sep 30 2007

"Since turning an incandescent bulb on and off doesn't shorten the life of its filament significantly, you " etc. http://members.trip...terslic/lights.html
[the dog's breakfast, Sep 30 2007]

[link]






       Do you have linky for light bulb shock?
the dog's breakfast, Sep 30 2007
  

       For domestic filament bulbs, the problem is that they run on AC. A capacitor will just charge and discharge as the polarity alternates - it won't work. You'd need some additional circuitry in the bulb (or switch).
MaxwellBuchanan, Sep 30 2007
  

       It should work. (+)
Shadow Phoenix, Sep 30 2007
  

       isn't this the complaint people have with low energy lightbulbs? (that they take time to fully light)
po, Sep 30 2007
  

       Google for "bulb saver" and you'll find a little thingy that fits under the bulb. It may not do any good, as the start-up isn't really the problem.   

       250ms isn't a noticeable-to-the-eye delay, is it?
baconbrain, Sep 30 2007
  

       A quarter of a second is noticeable, but seldom troubling in this application.
Texticle, Sep 30 2007
  

       //It should work. (+)// No, it shouldn't. See above. You can't just stick a capacitor across an AC-driven lightbulb, whether in the switch or elsewhere. It won't work.
MaxwellBuchanan, Sep 30 2007
  

       Most devices billed as "bulb savers" are just rectifiers - that is, they pass only one half-cycle of ac current, so the bulb is dimmer, and uses less power, and theoretically lasts longer.   

       There is a device called an "inrush current limiter," which is a specialized NTC (negative thermal coefficient) thermistor. This operates on ac or dc, but must be sized appropriately for the application. Essentially, this device has high (a few hundred ohms)resistance at low current, and negligable resistance (0.01 ohms) at operating current. Time constant is determined by the thermal mass.   

       If you like the romatic aspect of dim lighting, you can buy dimmers that automatically dim lights over a specific period (5-10 minutes.)
csea, Sep 30 2007
  

       If turning an incandescent bulb on and off doesn't decrease its life significantly*, is this idea bad science?   

       * I remain unconvinced.
Texticle, Oct 01 2007
  

       //* I remain unconvinced.// Bulbs have several failure modes. The commonest are:   

       a) Imperfect sealing, leading to gradual influx of air sufficient to oxidize the hot filament   

       b) Slow evaporation of metal from the hot filament in a vacuum   

       c) Mechanical failure of the filament; every on/off cycle causes expansion/ contraction of the filament (and, to a lesser extent, its supports), which will eventually lead to mechanical failure.   

       Manufacturers adjust the construction of the bulbs to balance these failure modes, and to give an expected lifespan that's best for them (not too long, not too short). In general, this means that mechanical failure (c) is the commonest mode of failure, though it's exacerbated by (a) and (b).   

       Mode (c) is made worse because the resistance of the filament is lower when it is cold - so there is an initial surge of current, which can lead to a brief overheating before everything settles down. This effect would indeed be eliminated by "soft" switches.   

       I can't honestly remember when I've seen a light bulb die while it was on in my own house - they always seem to fail when first switched on.   

       On the other hand, my mother's house had a bad mains supply (I guess it was at the end of a long line), and bulbs there would fail frequently, often while they were on - I think that's because the power fluctuated, effectively turning them off briefly now and again.
MaxwellBuchanan, Oct 01 2007
  

       So aside from the dodgy circuitry, it's good science?
Texticle, Oct 01 2007
  

       Yes to all three of those.
MaxwellBuchanan, Oct 02 2007
  

       [admin: I'm ignoring the widely known to exist, since this is different from a normal dimmer switch - it's an automatic process happening at turn-on/turn-off, not a brightness control. I believe this exists - csea's thermistor is pretty close - but isn't widely known or used in home applications.]
jutta, Oct 16 2007
  
      
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