I put up bug screens on some of the windows for the summer. They are a grey color (so they reflect more than black) and thought I'd check how much sun they block. I used a window on the southwest side with more than enough solar exposure. This is a double window and the screen is on one side, so this allows a relatively fair test. The windows also have light colored roller blinds (see
this post), so I checked their effect too.
I measured the temperature of the window sill and the blinds' surface (when down). The indoor temperature was around 21°C (70°F), outdoor 27°C (81°F).
| temperature °C (°F) | screen | no screen |
| window sill with blinds up | 24.5 (76.1) | 26.5 (79.7) |
| window sill with blinds down | 22.0 (71.6) | 21.9 (71.4) |
| roller blind surface | 27.8 (82) | 31.3 (88.3) |
So, in direct sunlight the bug screens reduce the amount of heat entering the room by about 2-3°C.