Team-BHP - Front windscreen sunfilm?

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Originally Posted by Sawyer (Post 1476778)

But the UV rejection is very high, close to 99% and so the dashboard fading will still be substantially less.

Quote:

Originally Posted by rkg (Post 1477320)

Windshield glass itself rejects UV. No need for film. Any glass sold in the market rejects UV radiation.

I too think RKG is right, or at least that windshields, as-is, cut enough of the UV radiation (primarily UV-A) to prevent transition lenses from working. Even if you place them in direct sunlight, right underneath the windshield, transition lenses don't work (you'll get a very very slight tint, nothing else).

As per wikipedia UV-A is primarily light at wavelengths between 320nm & 400nm. Apparently window glass blocks 90% of UV radiation below 300nm & allows 90% of UV radiation through, when above 350nm. Anybody got a UV meter ? :)

Quote:

Originally Posted by shajufx (Post 1477355)

If thats the case, all those who have installed V-cool or CR70 or Garware Icecool have lost their money ? I myself was considering Icecool for my windscreen as many have claimed better cooling and less glare. How do I decide now ?

i suggest you can put your plan on hold for sometime....coming to reducing the glare, buy an nice pair of Rayban sunglasses:-)

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Originally Posted by im_srini (Post 1477343)

As per this, if your lenses are using Silver Chloride (supposedly the most common material used for this purpose), shading difference can be interpreted as roughly the amount of UV below 386nm being blocked by windshield?:)

@shajufx and @knp, don't loose heart! UV doesn't contribute much to the amount of heat sunlight radiates. If their claims about IR/heat rejection are valid, then those films should be reducing heat, if not much of UV.

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Originally Posted by santosh.s (Post 1477593)

Hi Santosh, as per my understanding Silver halides are used in glass versions of transition lenses only - the ones I have are plastic.

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Originally Posted by santosh.s (Post 1477593)

UV doesn't contribute much to the amount of heat sunlight radiates. If their claims about IR/heat rejection are valid, then those films should be reducing heat, if not much of UV.

Yes, but it appears the windshield films do not do that too (see Sawyer's comments below)...

Quote:

Originally Posted by Sawyer (Post 1476778)

And remember that even they have a heat rejection of just around 55% - so the heat build up inside after a few hours will be not very different from naked glass.

The films are relatively pricey, so they must be working, but is the marketing mumbo-jumbo asking us to pay a lot for less ? Could a pair of shades be a better option ?

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Originally Posted by rkg (Post 1477320)

Windshield glass itself rejects UV. No need for film. Any glass sold in the market rejects UV radiation. No need for separate film. correct me if iam wrong

It is a marketing ploy used by sun film makers to sell

Sunfilm should reduce heat trasmission

You are spot-on RKG. Its a marketing ploy.
The glass itself cuts the UV transmission by 99%. That is why although you may be uncomfortably warm with bright sunlight streaming through, you will not be sunburned.

Interestingly, this is something I found on Llumar india website itself. "Less than 1% of the sun's ultraviolet (UV) rays penetrate the windshield in newer vehicles. This is due to UV absorption by the PVB (polyvinylbutyral) interlayer that is used to laminate two sheets of glass together, making up the windshield unit. Some vehicles five years or more years old may allow as much as 10% of the UVA to transmit through the windshield glass. (In some countries, windshields are merely tempered glass, with no PVB interlayer at all.) UVB is screened by the glass itself and UVC is screened by the ozone layer of the earth's atmosphere"
Source:Welcome to LLumar website

Further, as already mentioned on T-BHP elsewhere, the main contributor to the incoming heat energy is from IR and Visible light. And therefore the UV ttransmission cut mentioned by the Sunfilm mfgrs is nonsense!

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Originally Posted by psp62in (Post 1477646)

good info there on the UV. looking at few more sites, it seems quite obvious that the newer cars don't need front sunfilm for UV protection alone. older cars should still consider it.

so I guess the buyers (who still haven't plonked their money yet) have to decide whether the heat rejection (50%), IR rejection (97%) and glare reduction (23%) is worth the money or not. (referring to 3M CR70 specs).

The Main purpose of Windshield Sunfilm is for reducing heat and glare.
you can feel the difference once installing sunfilm.
I am using Xenos Panorama 60 Sunfilm in my windshield.though it's mainly used for buildings.
It's very efficient and cuts a lot of heat entering in to cabin.
AC is doing its duty pretty easy which boost mileage.

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Originally Posted by splitsecond (Post 1477568)

I am going to install v-kool on front glass in my spark, but the front windscreen already have company fitted tinted film(with 75% transparency) with black borders, so do i need to remove that inorder to install v-kool?

Split Second, windscreens and glasses of all cars have about 70-75% transparency.

All films are applied on the glass/ windscreen directly (even if they have the black borders which almost all cars have now) and what you're saying of removing film with black borders, I don't think it's possible and moreover one is not supposed to tinkle with that tinting.

By the way BHPians, is the transparency level of the glass (70-75%) related to Lamination or glass formation?

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Originally Posted by Sawyer (Post 1476778)

That is why it is necessary to go for the top spec film for this application. And remember that even they have a heat rejection of just around 55% - so the heat build up inside after a few hours will be not very different from naked glass. But the UV rejection is very high, close to 99% and so the dashboard fading will still be substantially less. Glare reduction will also remain at the same levels, much better than naked glass.

I did go for the top spec of Llumar film. It didnt seem to make any difference.

I think the key aspect is that after a few hours in the sun the heat build up will be about the same since 55% of the heat is going through, it should just take longer to get to the same heat level.

A scientific test would be to place two cars in the sun and measure the temperature every 5 mins till the heat level stabilizes. One car with the film and one without.

For short trips in the sun the sun film should help since it lets in less heat.

Basically in hot cities I would guess that the front film is a waste of money since the car is likely to be in the sun long enough that the heat in the car would be comparable to a car without sun film on the front windscreen.

/sanjay

Quote:

Originally Posted by san9jay (Post 1481347)

I think the key aspect is that after a few hours in the sun the heat build up will be about the same since 55% of the heat is going through, it should just take longer to get to the same heat level.

For short trips in the sun the sun film should help since it lets in less heat.

Basically in hot cities I would guess that the front film is a waste of money since the car is likely to be in the sun long enough that the heat in the car would be comparable to a car without sun film on the front windscreen.

/sanjay

Based on what I learn about the no additional benefit for UV ( welcome new learning for me!), the above sums it up well. After enough time in the sun, 45% heat absorption in India where the sun is strong, is enough to heat up the car to make it just as uncomfortable as one that has no film.
But the glare reduction is significant, and for those of us that have prescription glasses, even with transition lenses, this is still a very important benefit. I also suspect that it helps cut glare from oncoming headlights at night. I find that to be the case, and in which case, it is still a sensible accessory to install.

Sawyer and Sanjay,
I see your points. However, when it's hot you should be using the AC. I believe having sunfilms will surely reduce load on A/C, in the form of reduced fuel wastage, you may feel more comfortable and may be able to reduce blower speed by a notch. People may not bother much about fuel part, but comfort and reduced blower noise (better enjoyment of ICE!) should be worth it, I guess.