XJ Dreamin' said:
umm...isn't glass opaque to IR. The IR is radiated from surfaces in the room that absorb light - light of whatever spectum is coming through the window. It's the opacity of glass that causes the heat rise (greenhouse effect). Tinting the windows will reduce overall light entry to the room, thus reducing IR radiance within the room. Filtering UV will reduce sunburn.
Just keeping watch over the details. It's what I do
No, it is transparent (in typical forms. I'm sure there are some "exotic glasses" that are opaque to IR.) That's largely why you can start a fire with a magnifying glass - part of what you're focussing is IR "light" as well as visible. So, you're not only bringing all of the visible light to bear, but the
invisible light as well (although UV and the shorter-wavelength colours have less to do with starting the fire than IR, red, orange, yellow and the lower end of the spectrum.)
Essentially, what happens to heat up the room is that visible light and IR get in through the window, and are absorbed by objects within the room. Since the IR (
et al) isn't/aren't reflected back
out through the window, they become "local heat" and result in a noticeable temperature increase.
Ideally, you want to keep IR right out of the room as much as possible - thus, the mildly reflective window tint and/or reflective & insulating window coverings.
Ford, for a time, installed windows in the Sable and Taurus wagon that were impregnated with trace amounts of gold in the glass - to reduce IR transmission and keep interior temperatures down. It worked rather well - but it also resulted in $1500 windscreens, $300 side windows, and just generally drove the price of the vehicle up - leading to abandonment of the project after a few years.
Gold is simply the
most efficient reflector of infrared that is commonly available - which is why it was used. (Try pricing mirrors for LASER labs one of these days... Imagine a 2" round mirror costing upwards of $2000!) There are other solutions, but they will suffer a loss in efficiency relative to gold. You can use a reflective window tint (a/k/a "one-way glass") to reflect all light or IR, and that should keep temperatures down as well. Should also keep the neighbourhood Peeping Tom from seeing what you're up to as well...
Window tinting that results in partial absorbtion of light coming through the window will help the room - but you'll pick up some of the "waste heat" that is being absorbed by the tinting. If possible, you want a "reflective" window tint, which results in light
rejection instead of light
absorbtion. It's a small difference, but you should see it in your power bill...
