Fitting complete, (E) marked DRLs such as those sold by Ring and Hella is not a problem. Changing a filament to LED in an existing light is.
S130's experience is interesting. I think a LED is technically still illegal in a reversing light, but as they are not a required light and not on in normal driving it's very low risk. The fact the insurers asked the questions would make it hard for them to back down as it (sort of) validates the change.
Robert G8RPI.
On changing to complete (E) marked DRLs might be legal but it is still a modification that requires your insurer's approval.
As for my reverse lamp bulb change then yes it is interesting. They know I wanted to change it for the 30% improved brightness and that the existing setup is useless. Like you say the reversing lamp is not a legal requirement and is certainly not obligatory.
From the UK Vehicle Lighting Regulations we have:
SCHEDULE 14
requirements relating to optional reversing lamps
1. Number: Not more than two
2. Position: No requirement
3. Angles of visibility: No requirement
4. Alignment: To the rear
5. Markings–
(a) A motor vehicle first used on or after 1st April 1986 and a trailer manufactured on or after 1st October 1985: An approval mark
(b) A motor vehicle first used before 1st April 1986 and a trailer manufactured before 1st October 1985: No requirement
6. Size of illuminated area: No requirement
7. Colour: White
8. Wattage–
(a) A reversing lamp bearing an approval mark: No requirement
(b) A reversing lamp not bearing an approval mark: The total wattage of any one reversing lamp shall not exceed 24 watts
9. Intensity: No requirement
10. Electrical connections: No requirement
11. Tell-tale–
(a) A motor vehicle first used on or after 1st July 1954, provided that the electrical connections are such that the reversing lamp or lamps cannot be illuminated other than automatically by the selection of the reverse gear of the vehicle: No requirement
(b) Any other motor vehicle first used on or after 1st July 1954: A circuit-closed tell-tale shall be fitted
(c) A motor vehicle first used before 1st July 1954: No requirement
(d) Any vehicle which is not a motor vehicle: No requirement
Given that the underwriters in my case have given approval and reading all the regs above then I have a (E) light/lens/cluster with a non E bulb (not that bulbs are E marked) that is less than 24W and no intensity limit/requirement. On all these points yes I think the insurer/underwriters would have an interesting time in court were they to change their mind as I guess they would have so show that an (E) unit with a LED of power less than 24W exceeded and intensity value for which there is no limit.
HOWEVER when you read the Obligatory lighting requirements you can easily see how complicated it all gets with both statutory E Approvals coupled with minimum and maximum *candela* ratings and *intensity* ratings. This is a completely different ball game which is why obligatory lighting (be they bulb or especially LED) are heavily E regulated/approved.