If you need to use tinted lenses or sunglasses when driving, it is important to know how dark you are allowed to go to drive safely and legally in the UK.
| Filter Code | Light Transmission | Driving |
| 0 | 100 – 80% | Day or night driving |
| 1 | 80 – 43% | Day time driving only |
| 2 | 43 – 18% | Day time driving only |
| 3 | 18 – 8% | Day time driving only |
| 4 | 5 – 3% | Not for driving |
Sunglasses are typically category 2-3 with 20 or 25% transmission options. Category 4 tints are used for skiing or high altitude where UV is stronger and there is more reflected glare from snow and ice.