An amusement. The bow-tie spinner rotates when placed in bright sunlight on a counter or windowsill.

The two c))motion strips curl in opposite directions. When exposed to sunlight or a bright desk lamp, they uncurl asymmetrically, shifting the center of mass. So the spinner rotates.

Two strips are needed to cancel out any offsets created by variations in ambient temperature. That is, a hot summer day uncurls both strips symmetrically, so the spinner remains unmoved. It is the asymmetry of a light source which pulls one curl farther from the axle than the other.

It takes about 15,000 lux for the scoop to begin spinning. For comparison, full sun at noon is 100,000 lux. A bright desk lamp, about a foot away, also works. Note the scoop will start spinning at lower light levels than a desk radiometer.

Yes. See US Patent 6966812

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