Sun film on the Nexon EV: what Rule 100 actually allows, and what I run instead

Parking in open sun is the one thing that quietly eats my Nexon EV's range, because the AC then works hard for the first ten minutes of every drive. So sun film comes up constantly whenever we talk accessories.

Here is the bit most film shops skip over. Rule 100 of the Central Motor Vehicles Rules sets the floor at 70 percent light transmission for the windscreen and rear glass and 50 percent for the side windows, and you can read the actual wording here. Factory glass already sits close to that line, so a dark film layered on top puts you on the wrong side of a traffic cop's tint meter.

What I use instead is a folding windscreen shade plus app pre-cooling while the car is still on the wallbox, so that cooling load comes off the grid rather than the pack.

If anyone has tried a clear ceramic film and actually measured cabin temperature before and after, I would love to see those readings.