The whole idea of the ring was to reduce the copper required for the re-build after the second world war. It also reduces the number of fuses/MCB's required. In Europe there is a 16A Fuse/MCB for near every socket but the combination of the fuse in every plug and ring circuit means we only have one or two fuses/MCBs for the whole house in the consumer unit.
There is no benefit in making a ring circuit for a 5A lighting supply so although nothing to stop one making it a ring it is not normally done.
When one tried to read BS7671:2008 the word spur and radial seem to get swapped around a bit. In the old days there the cable was protected at source it was called a radial and where protected at destination it was called a spur but today we have fused spurs so hard to define.
So what ever the name if the destination fuse is the only protection for the cable (un-fused spur) then only one device is permitted be it a socket or FCU and the lenght is limited to 3 meters.
Where the cable is protected at the origin then you can branch off as much as you want.
There are other rules as to access and loop impedance and the BS7671 is written for all situations so in the house some interpretation is required. For example if you sanded the bedroom floor varnished and used a carpet less than room size so you could easy role it up then to make a hatch with some screws holding it down labelled junction box below with old round JB would likely comply. However change that carpet for a fitted carpet then you would first need to change that JB for a maintenance free type.
English does cause problems as you can have a series of lights which are connected in parallel and to write a reply to a question without some ambiguity is near impossible. So it is a balance between being pedantic and ambiguous.
Also some rules are strictly obeyed. ie Green/Yellow is only used for earth and never over sleeved but with blue it is often used for line rather than neutral it should be sleeved but often is not. In fact putting sleeves on Brown, Black, Gray is a pain easier to trace if you can see base colour.
So
I understand with sockets you are allowed one spur on a ring
is not correct you can have many more than one spur per ring the limit is one spur from each device on the ring. However since the thread was asking about lights it did not seem worth picking up on this.
It is near impossible for any DIY guy to install electrics following the regulations in the main because the test sets cost well over £500 to buy and even to hire around £75 and even if they did hire since every MCB size has different limits unlikely they would know the pass limits anyway. Add the that the dangers is using the equipment not sure if a good idea anyway.
So we try to answer near enough to the regulations hence you will often see where electricians disagree as to how the information should be condensed.
