[HN Gopher] Whitest paint is now thin enough to coat cars and pl...
___________________________________________________________________
Whitest paint is now thin enough to coat cars and planes
Author : bilsbie
Score : 46 points
Date : 2022-10-04 18:50 UTC (4 hours ago)
(HTM) web link (newatlas.com)
(TXT) w3m dump (newatlas.com)
| daveslash wrote:
| Re >> _" with an ability to reflect around 98% of incoming
| sunlight"_
|
| Seems like a mirror would reflect even more light. Now, obviously
| we don't want to make the exteriors of our buildings and cars a
| _mirror!_. but it made me wonder: What 's the difference between
| a _really really really_ white paint that reflects 98%+ light,
| vs. a reflective surface? Is it that the white paint reflects the
| light, but in a "scrambled" form, thus losing the image?
| GuB-42 wrote:
| To make things simple, yes, that's is. White "scrambles" the
| light, the correct term is "diffuses" but that's the idea.
|
| Maybe quantum physicists will disagree but the difference
| between a mirror and a white surface is that a mirror is
| perfectly flat and therefore will reflect light at always the
| same angle. It may absorb some of it, or even most of it (black
| mirror!) but what it reflects, it will do it always the same
| way.
|
| A white painted surface can be thought as a surface covered in
| tiny mirrors, all pointed in a different direction, and
| depending on which tiny mirror a ray of light will hit, it will
| be reflected in a different direction. With large pieces, like
| with a broken mirror, you will still see (as you said)
| scrambled images. But because the pieces are so tiny, you won't
| be able to make out an image and you will only see white. A
| glass pane can look like a mirror, but reduce it to a powder
| and it becomes white. It has nothing to do with absorption, you
| can have a 1% reflective mirror, and 100% reflective diffuse
| white.
|
| The way the "tiny mirrors" that make up the white paint are
| oriented give out its general look. Have them oriented mostly
| with the surface and you get a glossy finish, have them
| randomly oriented in many directions and you get a matte finish
| (this is called specular reflection btw).
|
| I've seen mirrors be called "smart white", it is white because
| it reflects most light in most wavelengths, and it is smart
| because it keeps the rays of light oriented.
| wffurr wrote:
| Yes, it's not reflecting the light so much as re-radiating it
| in a diffuse pattern.
| thehappypm wrote:
| I don't think there's a physical difference between
| reflection and re-radiation, is there? Reflection is just
| highly organized/non-diffuse.
| Fronzie wrote:
| reflection is coherent, a single physical process. The
| light keeps it's phase and polarization. Re-radiation is
| incoherent, caused by multiple particle interactions
| (physical processes). So there's quite a difference in
| physics.
| thehappypm wrote:
| Can you explain? As I understand it, in both cases, a
| photon comes in, gets absorbed by the material, and then
| gets re emitted.
| njdvndsjkvn wrote:
| yes. A white surface scatters the photons and a reflective one
| keeps them in the same position relative to the others. If you
| make a surface smooth enough it starts becoming partly
| reflective. There is also scattering of photons that happens in
| object itself
|
| I found this video about the topic to be interesting:
| https://www.youtube.com/watch?v=1n_otIs6z6E (title: Why aren't
| Mirrors White? Why isn't EVERYTHING a Mirror?)
| adrian_b wrote:
| Nope.
|
| Silver reflectivity is about 95%, aluminum reflectivity is
| about 90%.
|
| So the best metallic mirrors are worse than the best white
| paints, even if they can be better than the frequently used
| white paints based on titanium white (89.5% reflectivity).
|
| Total internal reflection might be closer to 100%, but that
| cannot be used for the light that comes from the air on the
| surface of a mirror.
| floxy wrote:
| You can have dielectric coatings on a mirror that increase
| the reflectivity to >99.9% (and over a wide range of
| wavelengths). You can of course get a lot more 9's if you
| only care about a narrow band.
|
| https://materion.com/products/precision-
| optics/application-f...
|
| https://en.wikipedia.org/wiki/Dielectric_mirror
| adrian_b wrote:
| 99.9% for visible light does not mean 99.9% for all the
| solar light.
|
| Most dielectric coatings absorb ultraviolet light so they
| reflect much less of the total solar light, most likely
| less than 90%.
|
| Such a mirror with dielectric coatings would not be able to
| cool the object on which it is applied, unlike the paints
| which are discussed in the article, which are based on
| boron nitride, barium sulfate, calcium carbonate or
| fluorinated polymers, all of which do not absorb
| ultraviolet light.
|
| The common white paints based on titanium white or zinc
| white also absorb ultraviolet light, so they cannot be used
| for cooling an object illuminated by the Sun.
| ben_w wrote:
| What I've seen says silver and aluminium are both a bit
| better than that.
|
| https://www.researchgate.net/figure/Reflectance-versus-
| wavel...
|
| https://www.researchgate.net/figure/Reflectance-of-Ag-Au-
| and...
|
| I think this better fits my observation that a clean mirror
| can easily be unnoticed in an environment similar in all
| directions, such as woodland or a messy room.
| adrian_b wrote:
| What counts is not the peak reflectivity from those graphs,
| but the integrals over the solar spectrum.
|
| Aluminum has lower reflectivity everywhere, but it retains
| a high reflectivity in ultraviolet.
|
| Silver absorbs ultraviolet, which lowers the integrated
| reflectivity over the complete spectrum.
|
| A few percent difference in the total reflectivity can make
| a large difference in the cooling power of a paint, but a
| few percent difference in the reflectivity of a mirror is
| unlikely to be perceived visually.
| ben_w wrote:
| Fair, I was only thinking of the visual spectrum and in
| this context that's not right. :)
| njdvndsjkvn wrote:
| A simple way to verify this is to observe that common mirrors
| also tend to be green, showing that the other colors are
| absorbed more by the mirror. If you face two mirrors towards
| each other you will see a lot of green.
|
| edit: here's an example: https://i.imgur.com/Ar80FYZ.jpeg
| adrian_b wrote:
| The common mirrors have the metal on the back side, so
| their reflectivity is diminished by the absorption in the
| glass.
|
| The better mirrors, which are used e.g. in telescopes and
| some other optical instruments, have the metal on the front
| side, but that limits the metal choice to aluminum, because
| silver is tarnished quickly by the sulfur compounds present
| in the air.
| njdvndsjkvn wrote:
| so why don't common mirrors just use aluminum? It's
| already cheaper than silver, right?
| adrian_b wrote:
| The common mirrors have been using aluminum for a long
| time.
|
| I do not know when aluminum has replaced silver, but it
| was probably not a long time after WW2.
|
| The silver mirrors had the advantage that the metal could
| be easily deposited from a water solution, anyone could
| make silver mirrors at home, if desired.
|
| The aluminum mirrors use a vacuum deposition process,
| which requires very expensive equipment, but the cost per
| mirror is much less.
| njdvndsjkvn wrote:
| Ah. I misunderstood your earlier comment. Thanks!
| bilsbie wrote:
| Couldn't this be revolutionary for spacecraft?
|
| Also would it make a better solar sail?
| detritus wrote:
| Colour me stupid, but in a simple white vs. black comparison,
| wouldn't a VantaBlack-clad solar sail absorb more energy, so be
| more useful?
|
| - ed I'm misunderestimating 'equal and opposite' photon
| reflections here, aren't I?
| twawaaay wrote:
| For solar sail you don't want to absorb, you want to reflect.
|
| When you absorb you only get half of the push (assuming
| reflective surface reflecting directly back at 100%
| efficiency vs absorbed heat that gets radiated
| omnidirectionally).
| ahazred8ta wrote:
| Boron nitride and barium sulfate pigment.
| crayboff wrote:
| I know nothing about this sort of stuff, but if this were applied
| to cars, would there be an increased risk of temporarily blinding
| other drivers on a sunny day?
| HPsquared wrote:
| It won't shine any brighter than the light that's hitting it.
| lpghatguy wrote:
| Like... the sun?
| twawaaay wrote:
| Still, snow can cause blindness:
| https://en.wikipedia.org/wiki/Photokeratitis
| tlb wrote:
| It reflects something like 98% of light instead of 90%, so the
| actual increase in reflected light isn't that big.
|
| Flat scattering surfaces are never blinding. The problem is
| with specular reflections off of shiny surfaces. Even though a
| shiny surface may only reflect a small fraction of incident
| light, it's all pointing in one direction which can dazzle
| observers.
| aliqot wrote:
| How does it affect white balancing on traffic cameras?
| tobyjsullivan wrote:
| > The new material features boron nitride in hexagonal
| nanoplatelet form and offers a solar reflectance of 97.9%
|
| What's the difference between white paint and a mirror? Scatter?
| zmgsabst wrote:
| Yep -- mirrors are coherent while white paints scatter, even
| though they reflect similar amounts of light.
| colanderman wrote:
| Yes, exactly.
| Ancalagon wrote:
| Very cool, but im skeptical about cost
| adrian_b wrote:
| With less than 300 grams of paint per square meter and a
| pigment made from cheap ingredients, it is unlikely to be more
| expensive than titanium white, but obviously this will be true
| only if it will be produced in large enough quantities.
| theandrewbailey wrote:
| If this takes over and is used everywhere, in 50 years, will
| people become nostalgic over titanium dioxide white? Will the
| titanium industry be supported by the few remaining vintage white
| paint manufacturers? \s
| twawaaay wrote:
| I think people will in fact get nostalgic about titanium
| dioxide white. Actually any white. Looking at the progress, in
| 50 years every surface is going to be covered with ads.
| c7b wrote:
| Are airplanes more in need of cooling or heating? The outside
| temperature at cruising altitude is around -50deg (roughly where
| the Celsius and Fahrenheit scales meet, btw), is the insulation
| good enough to just keep the inside at acceptable temperatures
| for humans?
| chuzz wrote:
| The article mentions airplanes waiting on the ground, but I do
| wonder what happens during flight. I suppose the engines create
| plenty of heat after all.
| [deleted]
| twawaaay wrote:
| It does not matter for airplanes. Both cooling and heating are
| in ample supply on an airplane.
| JoeAltmaier wrote:
| It's things like this that have the potential to have big
| effects. Savings to cooling will directly improve energy
| efficiency and thus CO2 production.
| gonz0p0litik wrote:
| Reflected heat has to go somewhere. Thermodynamics has not
| stepped aside in deference to our social philosophy.
|
| Every textile, screw, and drink cart on a plane is part of
| toxic industrial feedback loop.
|
| High five to us for externalizing on the future coping with the
| mess of our vanity projects.
| wffurr wrote:
| Back into space. Seems fine.
| njdvndsjkvn wrote:
| Back _towards_ space is more accurate. Some of the light
| will bounce back to the earth because of the greenhouse
| effect.
|
| edit: This doesn't mean that the paint isn't effective for
| what the researchers want it to do, in case that wasn't
| clear
| colanderman wrote:
| Yes, it goes somewhere where we don't feel the need to spend
| energy moving it away from.
| gonz0p0litik wrote:
| Into buildings and cities made of concrete and steel. So
| we'll spend less cooling planes and cars and more cooling
| urban areas. Oh but if we paint everything with it
| sunglasses sales will skyrocket! Buy Oakley!!
|
| This country gives zero fucks about the government storing
| kids in cages, why expect any better than "ignore and
| deflect responsibility to anything but my short term
| material comfort".
|
| The kids will have every right to drug us future old
| geezers up and sit us in front of an AI mumbling 2000s era
| white noise.
| colanderman wrote:
| Buildings subtend a very small solid angle relative to
| the earth and the sky most anywhere I drive (and I live
| in a major metropolitan area).
| jrockway wrote:
| I would assume that cooling buildings is more efficient
| than cooling small cars and planes. Buildings can, for
| example, use a ground source heat pump, which isn't an
| option for vehicles.
|
| I also have to assume that a perfect reflection from the
| top of a car or a plane just sends the radiation out into
| space.
| ceejayoz wrote:
| > Reflected heat has to go somewhere.
|
| Back out to space, where it came from.
| jamesgreenleaf wrote:
| If you mixed it with Vantablack, would you get the greyest
| possible paint? /s
| WallyFunk wrote:
| You could try buying some and find out!
|
| https://culturehustle.com/products/black-v1-0-beta-the-world...
|
| You could also mix it with the 'whitest white'
|
| https://culturehustle.com/products/white-20
| dfxm12 wrote:
| You linked to black 2.0. It may very well be the blackest
| black, but it is decidedly not Vantablack. I think this is
| worth distinguishing, because interestingly, I don't think
| just anyone can get their hands on Vantablack because someone
| obtained exclusive rights to it. :) https://en.wikipedia.org/
| wiki/Stuart_Semple#Conflict_with_An...
| twawaaay wrote:
| You can't mix Vantablack. It actually isn't paint, it is a
| coating grown through vapour deposition.
| RetpolineDrama wrote:
| The future is now, and it is blinding!
| chris_st wrote:
| Finally, we can make the city in Mirror's Edge [1] into reality!
|
| 1 https://en.wikipedia.org/wiki/Mirror%27s_Edge
| metadat wrote:
| How does this new paint compare to the contents of a spray paint
| can from Home Depot?
|
| Having a hard time searching the web for this one, the first few
| pages of hits are all about this new 98.1% paint.
| zmgsabst wrote:
| You're looking for something called "light reflectance value"
| or LRV.
|
| You can get 90-94% in wall paints; not sure about spray paints.
|
| https://www.kylieminteriors.ca/paint-colour-review-the-5-whi...
| crazygringo wrote:
| I know white clothing often contains "brighteners" which
| fluoresce, converting received UV light into visible wavelengths,
| so the resulting white is brighter than what is reflected in the
| visible spectrum.
|
| I'm just curious what role that ever plays in paint, if this 98%
| reflectivity is a big deal, or if we already have white paint
| with over 100% because of brighteners.
| adrian_b wrote:
| This 98% reflectivity refers to the total solar light,
| including infrared and ultraviolet light, because the purpose
| is to cool whatever is painted, despite being illuminated by
| the Sun.
|
| With fluorescent paints, the energy of the emitted visible
| light is always less than the energy of the absorbed
| ultraviolet light. The difference is heat that warms the paint.
|
| The paints discussed in the article also reflect the
| ultraviolet light. Moreover, they also emit infrared light in
| the frequency band where the air is transparent, and that
| infrared light leaves the Earth if the painted object is
| outdoors, which will be true for a building or for a car while
| it is used. By emitting more energy than it is absorbed from
| the solar light, the painted object is cooled (if it is
| outdoors).
___________________________________________________________________
(page generated 2022-10-04 23:02 UTC)