The 'matters of testing' site has a note on this from a couple of years ago, and the requirements for HID are auto self-leveling and headlight washers which are mostly lacking in retrofit units. They also referred to an 'LED headlight system', I think this has been clarified (tightened up) to include anything with an LED bulb in it. I'll add the link when I find it.
The current manual says this:
Vehicles equipped with High Intensity Discharge (HID) or LED dipped beam headlamps may be fitted with headlamp washers and a suspension or headlamp self levelling system.
Where such systems are fitted, they must work; however, it is accepted that it may not be possible to readily determine the functioning of self levelling systems. In such cases, the benefit of the doubt must be given.
Headlamp washers may work in conjunction with the windscreen washers (when the dipped beam headlamps are switched on) or by a separate switch.High brightness headlamp type approval requires washers/levelling I believe, so the test seems to be coming into alignment with that.
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This VOSA note effective 1/1/2012 is helpful, but it refers to an 'LED headlamp system' rather than 'LED bulb'.
http://www.partinfo.co.uk/files/MOT%20Changes%20-%20Lighting.pdf'Headlamp washing and levelling systems are mandatory for all vehicles fitted with LED headlamp systems ....'The draft May 2018 manual page 7&8 make it quite clear HID conversions are failures but LED bulbs seems to be a grey area, too many references to washers 'if fitted'.
At least reversing lights make their debut in the 2018 test, and there is some interesting clarity about
original fitment DRLs fitted to new cars from May 2018, which states
'DRLs may not operate when the engine is not running, or when the parking brake is applied, or when the park position is selected on automatic transmissions. 'Lastly in reference to Derms comment, even a halogen bulb might not be 'legal' if it's too bright which brings into question some of the 130% names given to replacement bulbs, 130% compared to what?
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TG