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.