Anthony 1, on 12 January 2010 - 18:55, said:

It is about time that manufacturers found something better than the pull down sun visor! ..... in this day and age some sort of photochromic arrangement should not be too far-fetched.

I agree with Anthony- can't they fit our yetis with :

BUT note:

"...An important note about photochromic lenses: because they react to UV light and not to visible light, there are circumstances under which the darkening will not occur. A perfect example of this is in your car. Because the windshield blocks out most UV light, photochromic lenses will not darken...."

We need to get our researchers on to this to sort it asap- calling all scientists / engineers and inventors ...to arms...

(and Aquarians - no offence meant- you are supposed to be light years ahead in terms of thought process /imaginations / inventions though than the rest of us mere mortals ! )

Check out these pages / web sites and read up on the info:

http://www.howstuffworks.com/framed.htm?parent=question412.htm&url=http://www.lbl.gov/Science-Articles/Archive/cheap-photochromics.html

http://photochromicwindows.com/index.html

In photochromic lenses, silver chloride (AgCl) and copper (I) chloride (CuCl) crystals are added during the manufacturing of the glass while it is in the molten state and these crystals become uniformly embedded in the glass as it solidifies.

The largest limitation in using PC technology is that the materials cannot be made stable enough to withstand thousands of hours of outdoor exposure so long-term outdoor applications are not appropriate at this time.

http://www.halfbakery.com/idea/Photochromic_20windshield

Invention Patent Strategies See If Your Invention Qualifies.

www.designmindgroup.com/action.htm

This invention relates to the manufacture of glass articles which exhibit photochromic behavior and which exhibit very high mechanical strengths through the development of a surface compression layer therein by an ion exchange process. More particularly, this invention relates to glasses wherein silver halide crystals impart photochromic properties and wherein the ion exchange involves alkali metal and silver ions.

WINDOWS OF THE FUTURE

New technologies are producing increasingly energy efficient windows. Already on the market are "super-windows," boasting triple layer designs, with two low-E coatings and spaces filled with mixtures of argon or krypton gases.

A new generation of windows, however, is being called "smart windows" because they adapt to changing conditions.

A few "smart windows" are already commercially available, and others are being developed in research labs. These windows change properties -- like their shading coefficients and visible transmittances -- in response to either an electric charge or an environmental signal such as a change in light level.

Depending on the mechanism that initiates the change in the window, these "switchable glazings" fall into four categories: electrochromic, liquid crystal, thermochromic, and photochromic.

Electrochromic Windows

Flip a switch and an electrochromic window can change from clear to fully darkened or any level of tint in-between.

The technology has been suggested for cars, where with a touch of a switch the driver can tint the mirror or sunroof. In buildings, the changeable windows allow for privacy, to cut down glare, and to ward off increases in solar heat.

The action of an electric field signals the change in the window's optical and thermal properties. Once the field is reversed, the process is also reversed. The windows operate on a very low voltage -- one to three volts -- and only use energy to change their condition, not to maintain any particular state.

To make an electrochromic window, a thin, multi-layer assembly is sandwiched between traditional pieces of glass. The two outside layers of the assembly are transparent electronic conductors. Next is a counter-electrode layer and an electrochromic layer, with an ion conductor layer in-between. When a low voltage is applied across the conductors, moving ions from the counter-electrode to the electrochromic layer cause the assembly to change color. Reversing the voltage moves ions from the electrochromic layer back to the counter-electrode layer, restoring the device to its previous clear state. The glass may be programmed to absorb only part of the light spectrum, such as solar infrared.

Early research indicates that the technology can save substantial amounts of energy in buildings, and electrochromic glazings may eventually replace traditional solar control technology such as tints, reflective films and shading devices.

Liquid Crystal Windows

The first commercially available "smart window," liquid crystal windows are used for privacy control. They do not provide energy savings.

In this window's normal "off" condition, the glazing is a translucent milky white. When an electric current is applied, however, it turns slightly hazy clear. The switch between the two states is nearly instantaneous.

The technology works this way: two layers of film enclose a layer of tiny liquid crystals. This assembly is laminated between two pieces of heat-treated glass. Both faces of the film are covered with a transparent, electrically conductive metal coating. These conductive coatings are wired to a power supply.

When the power is off, the liquid crystals are randomly scattered. Light entering the glazing does not have a clear path out, and the window is a translucent milky white. When an electric current is applied between the two conductive coatings, the liquid crystals align neatly and you can see through the window.

Other than the diffusion of light, the optical properties of the two states are nearly identical -- the window lets in nearly the same amount of light and solar heat whether it's on or off. Because there is little change in performance properties and because it requires constant energy to maintain its clear state, this liquid crystal window provides no energy saving benefits.

Thermochromic Windows

As the prefix thermo- implies, heat causes thermochromic windows to alter their properties. In response to changes in the ambient temperature, clear thermochromic glazings becomes diffused.

Several thermochromic technologies are being explored, but gel-based coatings seem to be the most promising. "Cloud Gel, " a product now on the market, is a thin plastic film that can be incorporated into almost any window assembly. The response temperatures of "Cloud Gel" can be adjusted depending on need and location.

In addition to automatically changing from clear to diffused in response to heat, the glazings also turn white and reflective, reducing the transmission of solar heat. That can reduce air conditioning costs significantly when it's hot outside. Because you can no longer see through the window once it loses its transparency, this glazing is probably best suited for skylights rather than view windows.

Photochromic Windows

Still in the development stage, photochromic windows respond to changes in light, much like sunglasses that darken when you move from a dim light to a bright one.

While this type of technology may seem like a good idea, it has its drawbacks for saving energy. Photochromic windows work well to reduce glare from the sun, but they don't control heat gain. That's because the amount of light that strikes a window doesn't necessarily correspond to the amount of solar heat it absorbs. Because the sun is lower in the sky during the winter months, for example, its rays may strike a window more intensely in the cold season than in the summer, when the sun is higher in the sky. In this case, a photochromic window would darken more in the winter than in the summer, although winter is the time when solar heat would be beneficial.

Another problem is that, while this technology works fine on small, eyeglass-sized pieces of glass, it has yet do be done successfully on a large-scale, commercial level for window-sized pieces.

Despite some problems, "smart windows" hold the promise of reducing energy demand and cutting air conditioning and heating loads in the future. They offer the next major step in windows .

Edited 13 March, 201016 yr by Lady Penelope

I find my glasses darken in the car!

I also found that my photochromic glasses darkened in the car - but this was a while ago. Maybe the wind shields of today filter out UV.

Why not make the top of the windshields photochromic?

The most annoying time for me is in the winter when the sun is naturally low in the sky. When we return home from visiting our family in Manchester, usually in the afternoon, the sun shines smack into our eyes. (WSW down the A55) Add the sun to salt spray and the mixture is devastating.

I usually try and delay the drive until the sun has set. I then rely on my "overpowered" (some say) halogens and the topped up washer bottle.

There used to be tinted strips that could be stuck on to the top of the windscreen. ( usually with TARQUIN and CHARLENE stuck on them) Perhaps someone will bring them back!

Anthony 1, on 12 January 2010 - 18:55, said:

It is about time that manufacturers found something better than the pull down sun visor! ..... in this day and age some sort of photochromic arrangement should not be too far-fetched.

I agree with Anthony- can't they fit our yetis with :

http://science.howst...question412.htm

BUT note:

"...An important note about photochromic lenses: because they react to UV light and not to visible light, there are circumstances under which the darkening will not occur. A perfect example of this is in your car. Because the windshield blocks out most UV light, photochromic lenses will not darken...."

We need to get our researchers on to this to sort it asap- calling all scientists / engineers and inventors ...to arms...

(and Aquarians - no offence meant- you are supposed to be light years ahead in terms of thought process /imaginations / inventions though than the rest of us mere mortals ! )

http://www.howstuffw...tochromics.html

Couldn't you get Parker vergel or Alan to sort something out?

Couldn't you get Parker vergel or Alan to sort something out?

I think the question was meant to be serious - don't you?

I think the question was meant to be serious - don't you?

No are you serious , what with litigation the way today it would never work . Police have light meters to check the amount of light passable through windscreen and side windows . wear sunglasses !

Ideally a photochromic area would be built into the windscreen and provide a level of darkness dependent upon the ambient light conditions. There will be some snags to overcome:

1. What proportion of the area of the windscreen do you make capable of becoming dark? You could link it to the position of the seat/steering column, which would mean extra sensors, though it would still be a compromise as people of the same height have differing leg/torso lengths.

2. How do you trigger the windscreen darkening? Light sensors are widley used in cars to activate automatic lights, also an old fashioned manual switch could be used.

3. Cost, usually the biggest snag there is. There will be an initial manufacturing cost and the possibility of higher insurance premiums. If the winsdscreen is thicker than the standard one, different body pressings may be required.

4. Safety. Todays cars have the windscreens bonded to the body, where they make a contribution to the rigidity of the body shell. Will these windscreens be as strong? What is its failure mode likely to be?, you don't want it failing and going dark during a night drive.

I should think that a manufacturer somewhere is looking at the problem, it's quite often Mercedes who are the first to introduce new ideas.

That just leaves the question, What's going to take the sun visors place as a place for putting car keys?

erm - sit on a cushion? (apologies for the levity!)

Top answer fordfan My thoughts in purple

Ideally a photochromic area would be built into the windscreen and provide a level of darkness dependent upon the ambient light conditions. There will be some snags to overcome:

1. What proportion of the area of the windscreen do you make capable of becoming dark? You could link it to the position of the seat/steering column, which would mean extra sensors, though it would still be a compromise as people of the same height have differing leg/torso lengths.

Could the glass be sensitive enough to determine angle of glare from heat sensor so only darken worst area?

2. How do you trigger the windscreen darkening? Light sensors are widley used in cars to activate automatic lights, also an old fashioned manual switch could be used.

see answer to above

3. Cost, usually the biggest snag there is. There will be an initial manufacturing cost and the possibility of higher insurance premiums. If the winsdscreen is thicker than the standard one, different body pressings may be required. Good point!

4. Safety. Todays cars have the windscreens bonded to the body, where they make a contribution to the rigidity of the body shell.

Will these windscreens be as strong?

Interesting consideration - But don't see why not?

What is its failure mode likely to be?, you don't want it failing and going dark during a night drive.

How often do sunglasses fail?

I should think that a manufacturer somewhere is looking at the problem, it's quite often Mercedes who are the first to introduce new ideas.

or Space research?

That just leaves the question, What's going to take the sun visors place as a place for putting car keys? I'm thinking about that one!

erm - sit on a cushion? (apologies for the levity!) Lady penelope says

Has the Rugby finished and do I dare ask how they got on?

Edited 13 March, 201016 yr by Lady Penelope

I find my glasses darken in the car! Lady Penelope says

I think the question was meant to be serious - don't you?

Couldn't you get Parker vergel or Alan to sort something out?

Parker says "yes M'Lady"

Lady Penelope says "Far superior... we have a Mod on the case...! "

the photochromic stuff on glasses is either incorporated into the glass or applied as an extra layer on top. Obviously changing the chemical composition of the glass will affect it's strength and other characteristics. If applied as an additional layer this may also lead to a change in strength especially as the screen is bonded to the car and if the layer is on the inside. If on the outside would it be durable enough given the use of windscreen wipers, getting gritted and being carpet bombed by seagulls.

My first thought about haing a glass sun visor was that it could be a bit nasty in an accident.

This does sound like an interesting idea and would be good if it could be electrically controlled and quicker than the stuff used in glasses, imagine the problems when you go into a tunnel or underground car park if it takes several minutes for the windscreen to lighten on a really sunny day.

A photochromic treatment was tried on windscreens some years ago I think by either Audi or Volvo, and was found to be too slow in reacting.

I seem to remember that the glass had the coating put on the inside of the outer layer, before it was laminated, so it didn't affect the thickness or strength, and was obviously protected. To be honest you are talking about a film that is microns thick so it really wouldn't affect any of these things.

The modern treatments, like on my glasses, are much quicker, and I rarely notice that they haven't lightened when I have gone into somewhere not bright.

There is an electrical system that can darken glass, or even make it opaque, that I have seen somewhere, and i think used micron thin LED's. Bet that would be expensive!!

In an attempt to aswer your questions:

Could the glass be sensitive enough to determine angle of glare from heat sensor so only darken worst area?

The glass could be split into zones, the characteristics of which could be adapted through the relevant controller via the diagnostic port. This would add complexity, which coupled with the mass production philosophy of building down to a price and not up to a standard, could put a question mark over its reliability and durability.

How often do sunglasses fail?

That's it, even something as simple as a pair of sunglasses can fail. They can get accidentally damaged just like a windscreen (stones and debris, not putting them in your pocket and sitting on them). Windscreens also have to contend with extremes of temperature and humidity and can de-laminate due to water ingress between the glass and plastic layers. Windscreens are also a primary safety feature (it helps to see where you are going), the merest hint of a series of failures and the press would make a meal of it, think of Toyota. I have seen reports on some BMW forums of failure of internal automatic dimming rear view mirrors, apparently the leaking liquid is not good for the leather upholstery.

Another problem is, how do you market it?, especially in a car that is perceived to be the budget brand of main stream manufacturer.

fordfan said-In an attempt to aswer your questions...

Thank you for your well thought through and considered replies fordfan

It looks like it's a good idea in principle...but practical issues make it too complex / expensive to resolve at present

We will just have to wait for technology to catch up with our ideas / wishes

either that or I'm going to have to re train...

(that may take some time!! I can't even seem to get my web links to stay as they should at the moment :'( - let alone contemplate molecular physics! )

Costs:

I think my glasses cost £15 to be treated 18 months ago, so how much bigger an area would you need on a screen? The top 6" by the width of the screen?

Even allowing for a cheaper price for bulk, I suspect it might be too expensive!!

Shame, it does sound like a good idea.

You can still buy those strips that fit along the tops of the screen, but now they seem to be mostly silver and used by the cruise fraternity!

the photochromic stuff on glasses is either incorporated into the glass or applied as an extra layer on top. Obviously changing the chemical composition of the glass will affect it's strength and other characteristics. If applied as an additional layer this may also lead to a change in strength especially as the screen is bonded to the car and if the layer is on the inside. If on the outside would it be durable enough given the use of windscreen wipers, getting gritted and being carpet bombed by seagulls. Yes I think there is agreement there- many points also raised by fordfan

My first thought about haing a glass sun visor was that it could be a bit nasty in an accident. Ouwch!

This does sound like an interesting idea and would be good if it could be electrically controlled and quicker than the stuff used in glasses, imagine the problems when you go into a tunnel or underground car park if it takes several minutes for the windscreen to lighten on a really sunny day. Yes :S

A photochromic treatment was tried on windscreens some years ago I think by either Audi or Volvo, and was found to be too slow in reacting. Seems to have been a good idea for years but no one has cracked it yeti!?

I seem to remember that the glass had the coating put on the inside of the outer layer, before it was laminated, so it didn't affect the thickness or strength, and was obviously protected. To be honest you are talking about a film that is microns thick so it really wouldn't affect any of these things.

The modern treatments, like on my glasses, are much quicker, and I rarely notice that they haven't lightened when I have gone into somewhere not bright.

There is an electrical system that can darken glass, or even make it opaque, that I have seen somewhere, and i think used micron thin LED's. Bet that would be expensive!! No good then :'(