[mrtksn]

>For example, we enlarged windows and doors, to the point were, standing behind one that's been cooking in the sun for a couple of hours, you feel the radiant heat a meter away from it.

There are window films that can block most of the light in frequencies which carries the energy and let the light from visible spectrum in, barely dimming the brightness and almost doesn't change the color.

I recently installed such a filter, I'm amazed everyday how the hot bright sun is so tamed once inside the house. Sometimes I open a window to let the full spectrum in just so I can put my feet on the spot of the unfiltered light and then on the filtered one and compare how hot it gets where the sun shines in full power and can barely heat once filtered. It feels like magic, like a winter sun that is bright but doesn't heat. The filter itself heats up like crazy, it even gets too hot to touch but heat transfer by convection doesn't do much.

My grandma lives in an old house built with thick stone walls with tiny windows. It stays naturally cool but I really like large windows. IMHO, the humanity has advanced enough to have large windows and still keep it cool. It's also good for the mood, some people like me really really like the sun and even the heat up to a point.

[voisin]

I have heard that if you install these filters on the inside facing pane of glass, the glass can crack as the heat builds up between the inside facing and outside facing panes of glass.

Have you found one that does not do this or do you have any comments about this risk?

[mrtksn]

Haven't had any problems so far. The film gets very hot, it's inside facing so I've touched it out of curiosity. I don't expect to have issues with it, unless the glass with the film does't have enough space to expand but my windows are European style UPVC so they are quite robust and well made. AFAIK there's an argon gas in the middle, must be well engineered and accounted for expansion.

[voisin]

This would make me nervous. Sure, things are holding up now, but what happens when that heat exceeds design tolerances on the seals? Does the warranty stand up if you have this film installed?

[throwaw1yyy]

Mind sending a link to the film you purchased? I have a large hot window I’ve been thinking of doing this to

[mrtksn]

The particular one I bought is this one: https://dropovercl.s3.amazonaws.com/21fa0b29-7858-4233-b895-...

It doesn't seem to be a real brand, Bauhaus sells it and its made in Taiwan. I'm sure there are similar or better films out there.

[tguvot]

proper architectural films with published specs (uv/ir rejection ratios, etc), not sold retail. at least i failed to find them

[magicalhippo]

We have the same in the windows we replaced in our living room. We took the least visible (and hence least IR blocking) option, which reduces transmitted IR with 60%. The coating went up to 90% IIRC though at that point it was a very visible blue. Ours has just a slight blue-green tint.

The difference this summer has been striking. In our bedrooms which are on the second floor, the sun feels hot through the windows. In the living room I can barely feel it.

We're up north so our home is well insulated, hence the summer sun tended to overheat the inside.

[mrtksn]

It's amazing isn't it? How was the winter with the filters on, if you have been through the winter of course?

[magicalhippo]

Not a full winter, but got most of last (installing living room windows in -15C is interesting). While of course it also reduces sun heat during winter, the sun is low enough during the winter that we only get maybe a couple of hours at best per day of sun. Given that most of the winter is cloudy or overcast to some degree anyway, we didn't notice the little heat we missed due to the IR film.

On the flip side, the glass we replaced was some 20+ year old two layer glass while the new were thick 3 layer stuff. They're vastly better insulating (heat and sound), so that alone was a huge plus compared to the old.

[zajio1am]

The disadvantage of such filter is that you want to get unfiltered light inside in winter.

[mrtksn]

It's supposed to help with heating too because it would block(by reflecting or absorbing?) the radiation from inside. I guess I will find out about it in a few months. If it's too dark in the visible spectrum, that can be an issue though.

[Waterluvian]

Generally speaking the surface receives about 1kw/m2. I’d love to see a spectral graph that shows how that kilowatt is distributed. How much visible light can you sneak for a very low amount of that energy?

[pistachiopro]

According to Wikipedia, 43% of the sun's energy at the surface of the earth is visible light (https://en.m.wikipedia.org/wiki/Sunlight#Measurement). So just blocking the other wavelengths would help, but I'm not sure it would be a "night and day" difference, so to speak. Daylight is several orders of magnitude brighter than normal indoor lighting, so I bet you could block 80-90% of visible light, as well, and it would still look really bright out while heating the inside significantly less.

[mrtksn]

I don't know the details but it worked out very well for me. It still lets some heating rays in but its much more manageable, some ventilation is enough now.

These photos shows how much the film dims the visible light: https://dropover.cloud/999162

The photo of the wall shows two areas, one area illuminated by the light passing through the filter and another small area illuminated by direct sunlight through the opening.

It's a window in a small room. The window has a top-open position which provides enough ventilation to take away heat that still manages to get in. Previously, this room was getting unbearably hot and now is much better(still hot on days with no wind though).

[lukas099]

Serious question: could you selectively block invisible light on the way in and *visible• light on the way out? Because that to me would be an awesome window.

[yorwba]

I don't think so, because light propagation is symmetric. If light can get in, it can get back out by reversing direction.

However, if you simply don't want to be seen by people looking in from the outside, there are still some options:

If the inside is much darker than the outside, light from inside is overwhelmed by light from outside getting reflected back (the operating principle of "one-way" mirrors).

If the window is covered with a grid that only has small gaps (e.g. window blinds), it's hard to recognize objects on the other side unless your eye is close enough to look through a single gap.

If the glass has a rough surface (i.e. frosted glass), light that makes it through is scattered in different directions, blurring objects that aren't very close to the window.

Various combinations seem possible. (Frosted glass window blinds?)

[lukas099]

Good answer. Thanks.