Here in Australia, Melanoma kills roughly 50% more people than car crashes. One of the primary places for UV exposure is sitting in your car. Can tinting the windows help? How much UV does automotive glass block, anyway? Find out here.
Warning: This segment is rated ‘S’ for ‘science’ and ‘T’ for ‘thermodynamics’. Sorry about that. (Occupational hazard.)
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THE GRIM FACTS:
Estimated deaths from melanoma in Australia in 2017: 1839
Road toll in Australia, 2015: 1205
Lots of people ask me about window tinting - last week, I got this:
“Is aftermarket tinting of any value? Our whole family is fair skinned. I believe the standard side windows are by default SPF 46 or 48 and custom darkest legal tint only improves that to SPF 50. Are these figures correct and if so what is the value of this accessory?” - Michael S
So - for those of you unfamiliar with ‘Straya: We love football, meat pies, kangaroos and … melanoma, sadly.
That last one’s a real problem, driving along mid-summer in our sunburned country in our shiny new … ultraviolet ovens.
Especially when you consider that the risk of death by melanoma is more than double the risk of dying in a car crash...
UV CRASH COURSE
UV light is invisible, and painless. You cannot see it or feel it. It's like The Force, in Star Wars ... only real, and (in a sense) malicious.
There are three flavours of UV light. UVC, which never really makes it to the Earth’s surface - it gets dissipated in the upper atmosphere ... so, it's not really a factor.
Then there's UVB, which is what causes sunburn - but isn’t that prolific.
And then there's UVA - the big one - 30 to 50 times more prevalent than UVB. Penetrates the skin more deeply. And has prison shower sex with your DNA, unpredictably.
UVA is what you bombard yourself with if you’re moronic enough to lie in a solarium.
There’s no case to be prosecuted that exposure to any of the flavours of UV is good for you. Especially if ‘you’ means you parking your caucasian/Celtic DNA in our sunburned shithole this summer.
AUTOMOTIVE GLASS AND UV
There are two flavours of automotive glass - laminated and tempered. Laminated glass is used for windscreens. Where glass is the bread, and a layer of polycarbonate is the filling. Happily, laminated glass blocks almost all UVA and UVB radiation.
Second flavour: Tempered glass - like the windows and rear screen on most cars. It’s just normal glass that’s been heat treated to toughen it up and introduce high residual internal stresses so that when it breaks it doesn’t form long shards that slice and dice you in a crash.
Sadly, tempered glass really only blocks almost all UVB radiation (the sunburn one). Unfortunately, tempered glass blocks only about 20 per cent of DNA-damaging UVA (the prolific one). In other words - it allows 80 per cent straight through.
And that’s just a rough guide - the actual amount transmitted depends on the composition and thickness of the glass - it’s not like there’s a mandatory standard for UV transmission and automotive glass.
So - you’re definitely better off driving with the air conditioning on, and the windows up. But if you are driving along and the sun is streaming through the side glass, you probably won’t get sunburn [UVB] but you are still being bombarded with about 80 per cent of ambient UVA [UVA, MELANOMA]. So that’s hardly ideal.
Does it not therefore suck that most sunroofs are tempered glass, and not laminated?
I mean, if the world were perfect, I’d take laminated, and banish both UVA and UVB.
Unfortunately, that’s not a choice available to even the scientifically literate contemporary new car buyer. I hate that.
And of course, if the sunroof were ever to break, it would be less explosive, and the cabin wouldn't fill up with broken safety glass ... so there's that.
TINTING AND UV PROTECTION
Credible tint films - from a business you could conceivably believe, like (say) 3M - make claims about UV protection. 3M says each of three of its automotive tint films (quote) “blocks up to 99 per cent of harmful UV rays” and for the other one it’s “up to 99.9 per cent”. It sounds pretty good.
Unfortunately, I don’t know what “up to 99 per cent” actually means. Last time I looked, it meant “less than or equal to 99 per cent” - which is hardly reassuring. I don’t know what “harmful UV rays” are, either. According to the Cancer Council, they’re all harmful.
I don’t know if this 3M “up to 99-whatever” business is just lawyers and their weasel-word bullshit, and/or generalised marketing department arse-covering and/or illiteracy. But it hardly inspires complete confidence in the product.
If you were to take these 3M claims in the most favourable inferential light possible, there is absolutely a case for window tinting if it could be guaranteed as a means of blocking all that UVA that the side glass is so good at letting through to ravage your DNA.
According to the Cancer Council:
“Clear or tinted films can reduce the amount of UV radiation penetrating through the side glass by over 99%” - The Cancer Council
According to 3M, one of its four automotive tint films are (quote): “SPF of over 1000” but two are only (quote): “SPF of up to 1000” - damn those legal and/or marketing bullshitters to the pit of hell. And the remaining one enjoys no SPF claims on 3M’s website. 3M also says those three products that do enjoy SPF claims are Skin Cancer Foundation recommended products.
The scientifically illiterate are pretty good at conflating visible light, heat and UV - but they’re different parts of the spectrum. So it’s worth noting that even a film that looks ostensibly clear - like the 3M Crystalline one - can allow 90 per cent transmission of visible light and still do the mad “up to 99.9 per cent” UV-blocking voodoo.
It’s also worth noting that while dark films are perhaps a bonus in the daytime, they might be a safety compromise at night. Which is why there are regulations.
Here in ‘Straya, there are only regulations for visible light on window films, not UV. It’s called ‘Visible Light Transmission’ or VLT. The minimum VLT is 35 per cent. In other words, tint films are not allowed to block more than 65 per cent of the visible light.
No tinting is allowed on the windscreen - not even a clear film - except on a strip up the top. In [BANJO STING] the Northern Territory 16 per cent VLT is allowed on windows behind the driver (so - second seating row and back from there). In WA and Queensland it’s 20 per cent.
If you breach the VLT specs in your state, and get pinged, the car is rendered unroadworthy, and then - in the immortal words of Gunnery Sergeant Hartman - you’ll be in a world of shit.
TINTING & SAFETY
I really don’t think there’s that much of a safety component to tinting. Dark films might reduce side vision a bit at night, but might also reduce fatigue during the day. In a crash where the side or rear glass is shattered it might mean there’s fewer hail-sized residual stress relieved glass particles being shot around thanks to inertia. The film might bind them together.
Right about now we’re on the cusp of another six months of summery hell, here in ‘Straya. So a key question among car buyers is: Will tinting make my car any cooler?
And the clear answer is: Not really. Tint film manufacturers - knock me down with a feather - make all manner of bullshit claims about cooling. Here’s one 3M prepared earlier.
“...rejects up to 97% of the sun's IR rays and rejects up to 60% of the heat coming through your windows.” - 3M
This is one of those bullshit claims that’s probably true - it’s just self-promoting and meaningless. Inconsequential is probably a better word. There are two main modes of heat transfer to and from a car - radiation and convection.
Radiation is from the sun streaming through the vacuum of space for 500 seconds, or something, and then belting into your car and turning it into an oven. And convection is the main mechanism for heat loss from the hot car - essentially bleeding heat off into the surrounding air.
That’s just how this works. Heat transfer for dummies: Eventually you get to a point of temperature stabilization - heat soak, if you like - where heat loss to convection equals heat load from radiation. (I’m simplifying this a bit, because the car also rejects heat by radiating.) Anyway - the thermometer is stable, ultimately, in respect of the air temperature in the car. Thought experiment time.
Summer. Hottest part of the day. The main radiant heat load is hitting the roof, not the windows. Therefore, the windows are not a major contributor to radiant heat load. They’re just not. Therefore, tinting can’t help much, even if it does block radiant heat. Tinting is also an additional layer of thermal insulation over the windows - and this will hinder convective heat loss.
Marketers are such bullshitters - the up until now undiscovered fourth law of thermodynamics. If tinting actually made your car cooler, 3M and its competitors would be doing umpteen tests that demonstrate this everywhere from here to Dubai and Egypt.
If you want your car to be cooler in summer - park under a tree. The leaves absorb solar radiation to photosynthesize. Or fit a small adhesive solar panel and run a fan that draws ambient air into the car to improve convective heat loss. Far more effective
CHOOSING A TINTER
You want someone credible doing the job of applying the film, if you decide to go ahead with getting your car tinted. Make sure they give you a guarantee, make sure they’re likely to be in business still, in three to five years - in case you need to make a warranty claim. Make sure they don’t exceed the VLT limitations in your state.
Make sure they use a credible film from a reputable manufacturer - not some cheap Chinese knock-off crap that looks suitably dark but which you have next to no way of knowing whether or not it actually blocks any UV at all. That’s kind of important.
Commercially, one of the ways a tinter can pump up his profit is using the lowest cost input materials he can. You don’t want that.
TINTING AND DEALERSHIPS
Finally, my number one tip is: Do not get the dealership to tint the windows for you. They’ll get the same tint guy you could get to do the job. He’ll drive over in his van and he’ll do it before you collect the car.
It’s the same tint, done by the same guy - guaranteed. The only difference is: The dealership will screw him down on price, and mark that same price up for you - by the traditional dealership parts and accessories margin of one billion per cent.
On special - this month only: We’ve slashed our margin on tinting down to just 500 million per cent. Don’t miss out. (That statement brought to you by honestadvertising.com.)
The dealership will of course dangle the carrot of wrapping this over-the-top tinting cost in the finance - so you can generate an even higher commission for the dealership, and pay even more, ultimately, for the tinting. Lucky you. See my tips on beating car dealers >>
Automotive glass does a decent - but not exemplary - job of blocking some UV. Unfortunately it does allow quite a lot of damaging UVA straight through. Tinting - with the right film - is certainly a hedge against that. The dark stuff for the rear glass - in the states that allow that - is a decent (but imperfect) hedge against prying eyes, too. And it could help in a minor way in a crash.
Blocking that UVA is the main rational reason for getting your car windows tinted.