Headlight regulations do exist and manufactures need to build cars which comply with the type approval ratings.
www.legislation.gov.uk
Interesting... Seems very light touch, with the main requirements for cars apparently being:
- 2 headlights, <400mm from the sides of the vehicle
- White or yellow light
- Between 500 & 1200mm off the ground
- For approved headlights, some requirements about settings for the horizontal cutoff of a beam and the middle of its beam pattern being between 1 and 2% below the horizontal in the recommended position when there is a single 75kg driver.
- For non-approved headlights the centre of the beam pattern needs to be below the horizontal, or set so as not to cause undue dazzle or discomfort to other road users.
- No requirement for wattage or intensity
More detailed come if your headlight is 'approved', with approved headlights meeting this regulation:
https://www.legislation.gov.uk/uksi/1979/1088/schedule/4/made
Which probably means meeting this:
https://www.legislation.gov.uk/eudr/1976/761/article/1
Which has been repealed and replaced with this:
https://www.legislation.gov.uk/eur/2009/661/contents
Which seems to link actual requirements for headlights, such as this:
https://webarchive.nationalarchives...XT/?uri=uriserv:OJ.L_.2010.177.01.0001.01.ENG
I've now lost motivation to read any further on that document or to read the separate documents for discharge lamps etc
, but it seems to have requirements about being able to illuminate certain zones within a range of lumen values, and for the 'passing' beam to provide adequate illumination without dazzle.
So I guess what this actually shows is that either enforcement of those rules is probably quite lax, or they need to be updated and expanded (given that many modern and presumably 'approved' headlights do actually cause dazzle in the course of providing their driver better than the required 'adequate' illumination for passing /dipped beams, and there don't seem to be strong enough requirements preventing full beams from being dazzling if automatic dimmers are used).