I'd posted more of a real world version of this question, involving greenhouses, a few days ago at... https://www.physicsforums.com/threa...rior-much-cooler-if-reflective-inside.875575/ ...but with no responses after 130 reads, I'm reducing it down to a barer and much better, IMO, hypothetical question here... Assume four hollow sealed clear glass spheres, let's say about 2 foot diameter each. Glass is typical thickness and transparency of single pane window, inside is just trapped air. Temperature of spheres and air inside and outside is the same, 70 degrees F, for all four spheres when first positioned outside in the morning before sun rise. Spheres then exposed to rising sun for hours, outside ambient air temperature climbs to over 100 degrees F. Question is; which sphere will have the highest internal air temperature and, most importantly, how significantly so compared to each other, if they vary in the following way... #1 sphere is as described above. #2 sphere is the same, except that it has a silver reflective coating on half of the inside of the glass and it stays positioned, relative to the sun, where that reflective coating is always on the bottom and sunshine is always streaming in on the clear top hemisphere. #3 sphere is the same as original in #1, no reflective coating, but it also has a 6" spherical lead mass painted black suspended by string in the center. #4 sphere is the same as #2 with the reflective coating and it also has the 6" lead spherical mass painted black suspended by string in the center. Air, inside and out and the spheres and lead mass all started out at the same temperature, 70 degrees F, before exposure to sun. I'd like to also assume, for this comparison to better isolate the radiant heat component, that there is no appreciative conductive heat transfer in or out through the glass itself for being in contact with the changing air temperature either outside or inside. What I'm trying to determine here is not just the ranking of, but the likely significance in the difference of, the comparative internal air temperature between all four spheres, while the sun is still shining on them all. For instance, likely expected difference between #1 and #2, is of greatest interest to me. Not looking for any number crunching and all, just a feel for how significant a difference might be expected between the two. Secondly, I'm curious how significantly the black mass might affect the internal air temperature, considering it is both intercepting and absorbing radiant heat that might have otherwise passed through the sphere, but is also still a heat sink for as long as it is still cooler than the rising internal air temperature via conduction. Again, solely the impact, and how significant, the black mass has on the internal air temperature is what I'm most curious about. Appreciate any thoughts.