back
37 comments
It's bizarre to call this "transparent", given that it highly distorts light, even if it technically allows most of it through. It's actually a translucent material.

This also makes it horrible for windows, since people expect to actually see out of a window, we don't use windows just as sources of natural light.

> This also makes it horrible for windows, since people expect to actually see out of a window, we don't use windows just as sources of natural light.

Not all of them. For some windows, the inability to see through is a feature not a bug. Privacy is a common reason to avoid transparent windows and giving up light is an unfortunate drawback. I’ve seen frosted greenhouses too, I assume the goal is to avoid lensing / ray effects going through the glass.

As such, getting more light and scattered would be advantageous in many situations.

In Japan, houses and apartments usually have at most one transparent window. The rest are heavily frosted. It took a while to adjust to that model but once I did I wished we did this more in the US. You get more light during the day, since clear windows don’t actually let in that much light unless the sun is shining directly in, then it’s usually too much light. You have absolute privacy — you can walk around buck naked without having to draw a curtain anywhere. And, unless you happen to be in the minority and have a killer view, frosted glass makes it less distracting to be indoors. Random stuff going on outside doesn’t steal your focus at all. The fact is that for most people there really is t much to look at out their windows — a crumbling street, the neighbor’s fence, the wall of the apartment building next door, a parking lot. But of course if you do happen to have a killer view, you can always have a clear window in that direction.
Oh the view's a good point, if your window faces the back of an other apartment building and all you have is a wall of AC you're better off with frosted glass.
I think it could be used for skylights in houses, but also commercial buildings. I've been in a few grocery stores where they use skylights to provide natural light but people aren't really worried about seeing the clouds and sky in a grocery store. It could be a good option there.
Skylights, conference rooms, privacy windows, decorative. Plenty of uses for this.
I don't understand why the article keeps saying it's more transparent than glass if it's mounted to glass. That's like wearing spandex under your parka to stay cool. I suspect there's something more coherent in the paper. Cool material though.
"These mini-pyramids scatter 73% of the light that hits them, which gives the material that frosted look. But despite that, it’s surprisingly more transparent to light than regular glass – 95% transmittance compared to the usual 91% of most glass. The team says that makes for a more comfortable lighting not just for people, but plants as well."

Clearly, because they're qualifying its frosting effect - it's frosted, which inhibits the passage of vision, but counterintuitively, it does not stop the transmittance of light, so it doesn't darken a room.

The parent's point is that it cannot increase the transmissivity of the material it's mounted to even if it is highly transmissive, thus in combination the composite will not be more transparent/transmissive than glass.
It will obviously deliver more total light if the structutred surface gathers more light than the flat surface.

If that's what's going on then it's no more mysterious than the difference between a cloudy day and a sunny day shining through the same pane of plain glass. When there is more light on one side, there is more light on the other side.

And that does seem to be the mechanism actually. Other commenters have pointed out this article just isn't very good and the original source never says transparent and does descibe explicitly that the surface is simply gathering more light by allowing less of it to reflect away. Light that would have reflected away is instead redirected inwards.

"Gathering more light" is generally proportional to its planar surface. In the case of a surface film the potential increase in projected planar area is minuscule.

If you imagine an incident ray, to have a material "gather more light", that ray needs to intersect the material whereas without that material it would miss the surface. By adding some amount of height the film may cause some rays to intersect the surface that wouldn't have (primarily around the edges) but that's going to be very very small.

In general its a safe assumption that any material of the same projected planar area you put in front of another material will reduce the total transmisivity of the system.

Normal glass reflects light (about 4%) at each air-glass interface. This material acts like an antireflective coating, reducing the reflection at the interfaces.
Perhaps compare this film on glass to other frosted glass methods which likely reduce the transmitted light far more.
The article talks about allowing more light into greenhouses, but the material also cools a room. One of the biggest reasons for greenhouses is to trap warmth for plants during cold periods. This might be fine for actively heated greenhouses, but I doubt it's the right choice for passive systems.
Greenhouses frequently get so hot they need to open their windows. I imagine that there is a sweet spot where a little less heating is worth it for the additional light hitting the leaves. It may be climate and season dependent.
Original article : https://www.nature.com/articles/s41467-024-48150-2
Having read that, I think the linked article is using "transparent" in a way that the original article never did, which is the cause of so many commenters' confusion.

The article never says the film is more transparent than glass. It says

> The average global transmittance of the PMMM in the sunlight spectrum range is 95%, surpassing that of glass (91%). This is because the incident rays reflected at the micro-pyramid’s surfaces can be redirected to the PMMM

My understanding (someone correct me if I'm wrong) is that this film cuts down on reflected glare, and redirects that light downward, so more light ends up going through the glass.

This makes the glass more translucent, which is the ability to pass through light, but not more transparent which I understand to be the ability to see clearly through glass.

You're right about what it does, but the original article also often calls this material "transparent", e.g.:

> This design integrates several functionalities, including light diffusing, self-cleaning, and radiative cooling, while maintaining a high level of transparency [emphasis mine].

Yes, but I read that as a "high level" relatively, compared to other solutions, not "more transparent than glass."
A better quote that I think illustrates that the paper was confused about the terms as well:

> The combination of these features makes PMMM a practical solution for transparent roofs and walls, offering improved light management, energy efficiency, and occupant comfort. Moreover, the use of readily-available, affordable, and environmentally-friendly polymer materials ensures the potential for large-scale manufacturing while remaining competitive with existing transparent roof and wall materials. Overall, the development of this multi-functional metamaterial paves the way for sustainable green buildings with enhanced transparency, energy efficiency, and occupant well-being. It contributes to the ongoing efforts towards creating a more sustainable built environment.

I think it's fair to summarize this as "a roof coated with this material would be more transparent than a transparent roof today", which is wrong. It could be interpreted as saying "by reducing the disadvantages of a fully transparent roof, this will encourage more buildings to adopt roofs that are not fully opaque, thus enhancing the transparency of roofs in buildings overall", but I think that's needlessly confusing.

Mods: Can we rename the title to "more transmissive than glass", even if that is not the underlying title? Half of the commentary here is focusing on that detail and it detracts from the discussion.
It may be more transparent than glass, but it's sitting on top of the glass, so it's not letting in more light. It only matters if it's better than other kinds of coatings you can get for windows now.
Yes, there is some confusion there. The point they are making related to plants though is that, apparently, (some?) plants absorb diffuse light better than direct light. So, they claim that the photosynthesis efficiency would actually be enhanced by applying this extra layer to the glass, even though it still reduces the total amount of light going in (they haven't directly tested this, but they estimate the effect based on some other papers which quantified the efficiency of photosynthesis in diffuse vs direct light).
Was confused by this as well.
Can glass be etched directly with these structures?
This is really cool! Would definitely purchase if it becomes commercial.

Does anyone on HN in/close to the materials space know what kind of timeframe it could take for this sort of thing to move from research development to industrial production?

"...reduce reliance on air conditioning" - that's gonna be amazing. But it is still hard to get fresh air...
Most air conditioning systems don't provide fresh air. They just cool the air already in the room/building.
It doesn't dehumidify, which is important. In hot and humid weather, dehumidifying improves comfort. It also prevents mold.

So that's a real disadvantage compared to a normal AC, which does dehumidify.

However, you could combine them. Install a smaller AC system that uses less energy. It will probably still dehumidify enough. You'd still save a lot of energy this way.

A modern "variable speed" AC system should be a good match because radiative cooling doesn't work as well on cloudy days. A variable speed system can scale up (provide more cooling power and use more energy) on those days, and on other days when radiative cooling works well, it can scale down but still run a large percentage of the time to keep humidity under control.

=-----=

Above I assumed when you said "fresh air" that you mean air that is dry enough to be comfortable.

But you might have meant literal fresh air, i.e. outside air to replace inside air with chemicals, smells, etc. For that, there's heat recovery ventilation (https://en.wikipedia.org/wiki/Heat_recovery_ventilation). It can transfer heat and humidity from one stream of air to another. So you can pump your cool and dry but stale air outside, and bring in hot and humid by fresh air, but you can transfer the heat and humidity from the incoming air to the outgoing air as they pass each other.

Yes, we need glass that is transparent to wind.
Its called Windows. But if you bought it from Microsoft , you will got creepers peaking you along with advertisements. And it crashes a lot.
You can do this today, and this would only work on a roof in that context.
It is interesting but I wonder how much it will cost to manufacture?
That sample seems quite a bit more opaque than glass
Yes, the right word would have been that it's a translucent material, not a transparent one. The paper makes this confusion as well, though they do sometimes call it "translucent" too.
It diffuses the light so the background gets blurry, but the light is more efficiently transmitted
Transmittance or translucency would be a better choice of words.