I'll admit, I wasn't as accurate as I should have been. I've corrected the part, but left out the long treatise about 2 and 4 byte instructions. Hopefully no one will miss it.

That's a neat feature I'll remember. Fixed as well.

FWIW, I've changed the font-weight to regular. It's the same size on my non-Retina displays, but increased to regular thickness on the high resolution ones.

Hopefully, it's readable for by everyone now.

Is it also unreadable at https://fonts.google.com/specimen/Lato ? (Try "Thin" at 18 px size)?

I'm not parent, but experiencing the same problem. Yes, it's also very thin at the google font site, on 18 px Thin. Here is a screenshot: http://i.imgur.com/bUe7gNs.png The arrow points to the "Thin" line.

Windows 10, Firefox 49.0.1

FWIW, I think it's a pretty common problem with many web fonts on certain platforms (windows?). I see it all the time.

Also, thanks for the post!

It's Lato Light (Lato @ font-weight: 300) at full #000, it's not a particularly obscure choice I think. I've checked the rendering on anything-but-retina monitors (27" at 1920x1080) but it looked fine to me.

Unfortunately, font rendering is still a bit of a crapshoot, it differs from OS to OS and even varies wildly between Linux distros (which may or may not use potentially non-free freetype functionality).

In the end, I hope it's manageable. We're open to redesign offers though =).