Comment by tzs
18 days ago
> Drivers in the UK must be able to read a number plate from 20 metres away, according to the Driver and Vehicle Licensing Agency (DVLA).
Unless I've botched the math and/or what the internet tells me about the size of the characters on a UK number plate is wrong this seems to be a bit overboard.
The internet is telling me that the characters are 79mm tall and 50mm wide (except for '1' and 'I') with a 14mm stroke.
My eyes right now are about 250mm from my monitor. Something that is 79mm tall and 20m away would have the same angular size as something 250mm away that is 79mm / 20m x 250mm = 0.9875mm tall.
If I set the size to 75% in Chrome that is the size of the numbers on this page in the timestamps and the submission points and comment counts. It is about 1/2 the size of the numbers in the text box that I'm writing this comment in.
I've just taken a photo of that and will include a link to it to show how small that is [1]. In that I'm holding a ruler next to the left side of the text. The "180" up where it says "180 points" is what you have to be able to read to pass the test. (If you can't see the photo because Imgur blocks your country just grab a ruler, hold it vertically 25cm in front of you, and the apparent size of the space between the mm marks is the size character you need to read).
I have no idea what road signs and markings are like in the UK, but in the US in ~50 years of driving I don't think I've ever needed to read anything anywhere near that small.
I'm sorry to say your conclusion doesn't hold. I'm not sure where exactly you went wrong, without trying to do the math my best guess would be that you just can't properly simulate a far-sight task in a near-sight environment like that. Our eyes don't work that way.
But if you go outside and do a real world test, you'll (hopefully) find that a number plate should be readable from much further away than 20 meters. If you don't, please go and see an optometrist! I'm serious.
20 m is actually a very lenient requirement IMO. In my country, one should be able to read a number plate from about 35 m easily, and with good eyesight, 65 m and more shouldn't be a problem.
Someone with 20:20 vision can read a UK number plate from about 60m so the 20m standard allows for some eye imperfections. You're allowed to use glasses.
I have some experience because I got a macular hole in one eye which had surgery. With the good eye I can do about 60m, with the problem one about 20.
if you're expecting a response from someone in the UK, use something other than imgur.com