Clear Solar Power Crookes Radiometer Sun Light Energy Spinning Vanes

I purchase these raidometers as gifts. Before issuing them i test them for rate of spin. I have a very good working model and that is the base sample for rate of spin from a given level of light. I recently received a unit that did not meet standard and will return it. In all, I must have bought at least 15 of these units and only two were returned. In bright sunlight they should spin like crazy. If they are making 60 RPM in brught sunllight I consider that poor quality control. I will continue to purchase these units because they are well built but maybe it is the level of vacuum or the one point bearing and excessive resistnce that is at fault. Overall I do like this unit but will not hesitate to return a poorly performing unit.Update: The unit that works ell spins clockwise when viewed from the top. The recent purchase units that were returned are spinning counter clockwise. The construction is good but minor flaws are acceptable. It is the rate of spin that is the issue. If they spin slowly, or not at all, I return for replacement. Slow is 60 RPM or less in direct sunlight. The unit that works well must be spinning aboout 200 RPM, maybe 300. One looks sick and the other is performing at the Olympicc level.

It’s sitting in bright sunlight but there is no spinning indoors. Just a little wobbling. I took it outside, and it spun like a top. Very cool gadget. Guess my thermal windows are working well 😁

I often look at this object on my kitchen window-sill, and like it when it "comes alive."

I didn't think it was much, but it turns out it fun to watch during the day. Morning with direct sunlight it spins really, really fast, later with indirect light just fast, at sunset it wobbles around.

Looked great. But didn’t work

As other reviewers have noted, the radiometer arrived with some of the black paint flaking off one of the vanes. The rotor is also out of balance so it wobbles at high speed when n direct sunlight but compared to one I got in Germany about 8 years ago, it spins a lot faster.

Cool toy. I’d buy again

Pushed by photons (light)? - No.Hint: Photons have no mass, therefore no "push" effect. Those little photons do possess energy though.So, intelligent people would ask, "So what does push the vanes?".Ans: The globe is almost a vacuum so there is a very small amount of gas inside. The rotating forcecomes from that gas being heated by infrared radiation (you can put something hot near the radiometer and it will spin with no visible light) with the black side of the vanes absorbing more energy and becoming being hotter than the white or silver side. I will not go into detail here, but the hotter gas is repelled off of the black side which creates a slight positive pressure, and the gas from the cooler white side migrates over the edge to the black side (creating a slight negative pressure on the light side) and replaces the escaping hot gas from the black side increasing the pressure slightly there. Most of this action occurs right near the edges of the vanes. Therefore, more pressure develops on the Black compared to the Silver side! Got it? Whew! Don't feel bad if you didn't figure this out. It took several great physicists many years to figure this thing out (including Einstein).OK, not 100% correct? You physics experts can correct my explanation. Thank You