Time for a quick Jihad on bullshit: the top 10 things you need to know about window tinting.
Good idea or not? That’s next. Warning: This segment is rated ‘S’ for
‘science’ and ‘T’ for ‘thermodynamics’. I’m very sorry about that. Occupational hazard.
I’m John Cadogan from AutoExpert.com.au – the place where Aussie new car buyers save
thousands off their next new cars. Without face-to-face car salesman brain damage … unless
of course you really want that. We could arrange it, hypothetically. It’s just nobody’s ever
asked for that specifically. Hit me up on the website if you want a new car cheap. In
‘Straya. That’s what I do. 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?” So – for those of you unfamiliar with ‘Straya:
We love football, meat pies, kangaroos and … melanoma, sadly. And that last one is
a real problem, driving along mid-summer in our sunburned country in our shiny new … ultraviolet
ovens. There are actually three flavours of UV light.
UVC, which never really makes it to the Earth’s surface – so, not really a factor. UVB, which
is what causes sunburn – but is not that prolific. And UVA – the big one – 30 to 50 times more
prevalent than UVB. Penetrates the skin more deeply. And then 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 a good idea. Especially if by ‘you’ it means you parking
your caucasian/Celtic DNA in our sunburned shithole this summer.
While we’re talking flavours: 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 enough, laminated glass blocks almost all UVA and UVB radiation.
The second flavour: Tempered glass – like the windows and the rear screen on most cars.
It’s just normal glass that’s been heat treated. That toughens it up and introduces
high residual internal stresses so that when it breaks it does not form long shards that
slice and dice you in a crash. That’s bad… 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 (that’s the prolific one). In other words – it allows 80 per cent of
UVAmore or less straight through. And that’s just a rough guide – the actual
amount transmitted depends on the composition of the glass and the thickness – 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 but you are still being bombarded with about 80 per cent of ambient
UVA. So that’s hardly ideal. Does it not therefore suck the big one 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. And I hate that.
Credible branded 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”. So that sounds pretty good.
Unfortunately though, 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. Because, 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 of that UVA that the side glass is so absolutely 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%” 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 designation 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 actually from 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 tint 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 windscreens – not even a clear film – except in a strip up the
top. In 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. I really don’t think there’s that much
of a safety component to tinting. Dark films might reduce side vision a little bit at night,
but might also reduce fatigue during the day. In a crash where the side or rear glass gets
shattered it might mean there’s fewer hail-sized residual stress relieved glass particles being
shot around inside thanks to inertia. The film might bind them together. Just like The
Force. 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 the best word for it. There are two main modes
of heat transfer to and from your car – radiation and convection.
Radiation is from the sun streaming through the vacuum of space – those photons – 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 or cooling 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 – you might call
it heat soaking, where heat loss to convection equals heat load from radiation. (And I’m
simplifying this just a bit, because the car also rejects heat by radiating.) Anyway – the
thermometer is stable, ultimately, in respect of the air temperature inside 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 contributing factor in a major way 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 – 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 – just 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 from within. Far more
effective If you decide to go ahead with getting your
car tinted you want someone credible doing the job of applying the film. Make sure they
give you a guarantee, and 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 no way of knowing whether or not it actually blocks any UV radiation. That’s
kind of important. Commercially, one of the ways a tinter can
pump up his profit is using the lowest cost tint film. The input materials, right? You
definitely don’t want that. Finally, my number one tip is: Do not get
the dealership to tint the windows for you. They get the same tint guy you could get to
do the job. He’ll drive in, in his van and he’ll do it before you collect the car.
It’ll be a convenient exercise. It’s the same tint, done by the same guy
– guaranteed. The only difference is: The dealership will screw him down on the price,
and mark up that same price up for you – by the traditional dealership parts and accessories
margin of one billion per cent. On special – this month only (perhaps): We’ve
slashed our margin on tinting down to just 500 million per cent. That’s 50 per cent off.
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 even higher commissions for the dealership there,
and pay even more, ultimately, for the tinting. Lucky you.
In conclusion: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 very minor way in a crash.
But blocking that UVA is the main rational reason for getting your windows tinted. Up
to you. I’m John Cadogan – thanks for watching.