[M235ForNow]

Anyone have information on how much factory UV block exists on the 2 series side windows? I'm told it comes from the factory with some degree but it feels pretty intense from the sides and I'm looking for any way to reduce the heat/UV and not violate CA standards.

[albertw]

This was an important issue for me since I have a mild case of vitiligo. The sales manager checked with the head office and assured me it has effective blocking for both UV A and UV B. The glass itself is good enough for UV B, and I was wondering whether to have a plastic film applied to block UV A. I had already purchased the car so I think there is no reason to disbelieve the information about UV A.

Since no protection is perfect, I try to wear protective clothing when I know I'll be driving for several hours with the sun shining on me, and I use the (pathetically short) sun visor to block the sun whenever possible.

[B58togo]

Standard factory glass allows 70% light transmittance.

[CP911]

I haven't checked my 2er, but I want to say I've seen the UVA/UVB protective info etched in the windows before on a previous car of mine. Just can't remember which one it was now. Pretty sure you are good to go here with the bimmer.

*edit* Found this local news article online:

"The layer of plastic helps windshields absorb nearly all of the sun's ultraviolet rays. Plastic is naturally good at absorbing UV rays, Dishart says, and can be made with extra UV absorbers to protect even more. He says windshields absorb 100 percent of UVB rays, which cause sunburn, and around 98 percent of UVA rays, which don't cause sunburn but can do long-term damage to the skin.

That gives windshields a sun protection factor — or SPF — of 50 or more, the equivalent of some of the strongest sunscreens, Dishart said.

Sunroofs, too, often contain UV-absorbing technology that can block around 90 percent of UV rays. That's partly to keep the car cool as well as protect occupants from sun exposure.

But side and rear windows are a different story, and their SPF can vary a lot depending on the vehicle.

Side windows are usually made from cheaper tempered glass, which is around 4 millimeters thick and doesn't include a layer of plastic. Tempered glass is designed to shatter into tiny pieces, to protect the occupants in a crash. But unless they're tinted for privacy, side windows usually absorb only 65 percent of UV rays. That gives them an SPF of around 16, Dishart says, the same as some of the lowest grades of sunscreen."

Source - https://www.tampabay.com/news/health...he-sun/2139733

[albertw]

I don't recall the exact SPF of side glass, but 16 sounds about right. (Dermatologists usually recommend 15 as a minimum.) However, that means the glass blocks a lot more than 65% of the UV B. It blocks 15/16, or 94%.

The problem with SPF is that it applies only to UV B. Ten times as much UV A as B reaches the ground, and glass stops very little UV A. It's not clear where the 65% came from, but it's probably based on the total energy of the UV that gets through the glass (since each photon of B has a lot more energy than A).

Some things to be aware of if you're concerned about UV exposure (as I am):
- UV B is mostly responsible for burning
- UV A is mostly what stimulates tanning
- Clouds stop UV B but very little UV A.
- The cancer causing potential of UV A is about 1/10 that of UV B, but there's 10X as much so they are equally dangerous.

[albertw]

I bought a UV meter and used it to check the dealer's statement that the side windows of my M240i have an added UV barrier. The bottom line is that they don't have much, if any. Here's the details:

Meter: General UV 513AB, which measures both UVB and UVA and gives the result in rate of energy detected per unit area. The manual includes a sensitivity curve and it is quite non-linear, with UVA detected approximately three times more efficiently than UVB. However, in terms of biological effectiveness it's roughly the reverse*. UVB is given about 3X more weight than UVA in the meter readings.

The sun is still fairly low here, so direct sunlight at noon gives a reading of 6500 microwatts per square cm. The windshield transmits 1% of that. The side window transmits 11.5%.

For comparison, my prescription glasses, which have a UV coating, and the faceshield of my Arai helmet (for which Arai makes no claims about UV) both transmit 1.4%. The side window of our RAV4 transmits 11.8%, and Toyota makes no claims about a UV barrier on their side glass. Ordinary glass of about the same thickness (door from a bookcase) transmits 52%.

I think this means that the type of glass in the side windows, including the tint that blocks 30% of visible light, is about 4.5 times better than ordinary glass at blocking UV, but there is nothing special about the glass in the side windows of my M240i. Unless the RAV has the same, rather ineffective UV barrier, I think the dealer was misinformed by BMW Canada.

*Photons of UVB have enough energy to damage DNA directly, while UVA photons can damage DNA only by damaging other molecules which then can react with DNA, which is roughly10X less efficient than direct damage. Also, there is on average 20% more energy in each UVB photon.

[albertw]

I want to add some plastic window tint to increase the UV protection of the side windows. I'd like there to be no edge visible, which requires raising the window after the door is open. Is there an easy way to do that?

I can't see any switch that tells the computer to raise the window after the door is closed, so I assume it is attached to the latch system and hidden inside the door. The only thing I can think of is disconnecting the battery, then opening the door.

[snaketh]

Has anyone ever been ticketed in CA for tints? 80% of the tinted cars I see are illegal, cops don't seem to give a shit, at least here in LA.

[Winemaker2]

They used to care and I received fix it tickets a couple times which was frustrating when you could barely tell there was any additional tint. Police seemed to pick on Porsches and BMWs. In NorCal they also loved pulling you over for no front license plate. I agree it appears the police have more important things on their agenda unless you get caught speeding and then everything on your car is up from grabs.

[albertw]

[QUOTE=albertw;24565485]I want to add some plastic window tint to increase the UV protection of the side windows. I'd like there to be no edge visible, which requires raising the window after the door is open. Is there an easy way to do that?
QUOTE]

Since there were no replies, I suspect no one else worries about this. In case someone does, I'll post my solution.

The tint installer said he would remove the molding at the bottom of the window to let him coat the entire glass area that is visible when the door is closed, but I was reluctant to let him do that. It turns out that if you open the door, then push the latch closed the window rises back up. If you touch the handle as if you were opening the door, the window drops back down and you can close the door normally.

[Winemaker2]

I had a BMW dealer repair shop install and they had to pull the door panel away along the top edge to get full coverage. I believe they disconnect the battery or reprogram the window so it does not move when opening and shutting the door.