Half a croissant, on a plate, with a sign in front of it saying '50c'
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Powerless automatic blinds

Blinds that close themselves when it gets dark
  (+6, -2)
(+6, -2)
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The idea is for Venetian blinds to be open when it's sunny out/darker inside, for lighting, and then be closed when it's dark out/lighter inside, for privacy. Instead of rigging up stepper motors and light sensors, though, it would be great if the blinds were made of a material that folded up on their own simply because of the difference in light from one side to the other.

I'm not sure if this could be done with a clever application of bimetallic strips. Presumably you'd need to make the strips respond mostly to heat from radiation (which would be different from one side to the other) and not to heat absorbed from the air around them (which would be the same on both sides), which would make things difficult.

Phototropism of plants seems to be too complex to mimic.

Maybe there is another substance/design that would respond to the light itself, instead of heat?

I've baked a quarter of it, at least.

omegatron, Jan 03 2007

Mathilda lampshade http://www.superfam...e/doc/mathilda.html
The lampshade bends out and opens up by the heat when the lamp is turned on [omegatron, Jan 03 2007]

Wax in a piston http://en.wikipedia...ermostatic_elements
[goldbb, May 18 2009]

My current solution Mercury_20Windomirometers
It SEEMED so obvious. [WcW, May 18 2009]

[link]






       I don't think bi-metallic strips need a temperature gradient, but they might be colder during the day in winter than on a summer night.   

       Using light directly: Maybe use the photoelectic effect to charge the material during daylight, then somehow use self-repulsion or attraction to other stuff so it moves the right way.
caspian, Jan 08 2007
  

       Unpowered automatic windows are available for greenhouses, so the principle of moving a reasonably sized object with heat changes is sound. It may not transfer well to houses as we smooth out the large day/night temperature differences with insulation and heating. [+]
st3f, Jan 08 2007
  

       How do greenhouse ones work?
caspian, Jan 08 2007
  

       // Maybe use the photoelectic effect   

       I believe that would only be useful in a vacuum?
omegatron, Apr 03 2007
  

       Re: caspian They have a piston with wax inside that expands and pushes the rod out like a hydraulic cylinder.
AnotherBrian, May 19 2007
  

       If the insulation is a problem, maybe have a place for the wax uninsulated from outside but insulated from inside.
caspian, May 26 2007
  

       How about a wax thermostat device?
goldbb, May 18 2009
  
      
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