The law on trailer light wattage

[BertBert]

I have got a new to me BJ trailer to tow the race car. In sorting out the lights (new plugs bulbs etc), the tail lights seem to be single bulbs rather than combined stop/tail.

Both are broken, one is 5w the other is 10w. I assume there is a correct wattage? Anyone know what it is and where it's defined?

Cheers
Bert

[rambo19]

Get LED clusters for the trailer.
http://www.ebay.co.uk/itm/Pair-12V-Rear-Stop-LED-L...

Something like the ones above.

[N Dentressangle]

There's no wattage requirement in law:

http://www.legislation.gov.uk/uksi/1989/1796/sched...

They're usually 5w though, in my experience. It depends what the wiring circuit is designed to take.

[TooMany2cvs]

Tail lights are normally 5w. 10w might improve visibility, but reduce the distinction with brake lights. There should be side markers, too.

Brake and indicators would normally be 21w.

[BertBert]

Thanks, I think I'll go for 5 then.

The LEDs look nice, what's the advantage over bulbs?

Bert

[N Dentressangle]

Brighter
Last longer
Lower current draw

[TooMany2cvs]

BertBert said:

The LEDs look nice, what's the advantage over bulbs?

Bling visuals apart, lower power draw and - for brake lights - faster response. Indicators may not draw enough for the bulb fail warning to play properly.

[BertBert]

TooMany2cvs said:

Bling visuals apart, lower power draw and - for brake lights - faster response. Indicators may not draw enough for the bulb fail warning to play properly.

All good, I don't have bulb fail warning for the trailer anyway. It's wired in with a generic relay box rather than clever VW wiring.

I like the idea of lower current draw as well. The ones linked fit nicely in the hole, so I will order a pair. The only thing that puts me off is joining the wiring as it'll be exposed and joins always seem to go wrong eventually.

Bert

[paintman]

Assuming standard bayonet fitting bulbs use the same wattage as on a car:
Rear sidelights single filament 12v5w
Stoplight single filament 12v21w

LEDs usually longer life, but can confuse some vehicle's electrical system due to the low draw and need to be fitted the right way round - by that I mean polarity, if you put one in & it doesn't work, refit after turning 180deg & it should work. Don't use coloured ones behind a coloured lens.

ETA For exposed wire joints use an adhesive lined crimp connector. Crimp then heat with a hot air gun, shrinks the tube & you'll see the glue appear at the ends of the tube. Work fine on my boat!
These: http://uk.rs-online.com/web/p/crimp-butt-splice-te... also sold in small quantity packs at Halfords etc.

Edited by paintman on Friday 6th February 12:51

[Dr Mike Oxgreen]

paintman said:

Don't use coloured (LEDs) behind a coloured lens.

Not quite sure what you're saying here, but if you're saying you should use white LEDs behind a coloured lens then that is most definitely incorrect advice.

Unlike a conventional filament bulb which shines a wide mixture of frequencies, a red LED shines all of its power in red-frequency light, nothing else. So if you put it behind a red lens (which lets through only red light) then all the power of the LED goes through the lens, which is exactly what you want.

But roughly speaking, a white LED shines only a third of its power in red-frequency light. The rest is blue and green. If you put that behind a red lens, it'll filter out all the blue and green light and only let through the red light - which is only about a third of the LED's power. Two-thirds of its power has been wasted.

So for tail lights and brake lights you should always buy LEDs that shine red, regardless of whether it's going behind a red lens.

Similarly for indicators you should try to buy LEDs that shine amber, regardless of whether your indicator lens is coloured.

Edited by Dr Mike Oxgreen on Friday 6th February 14:06

[TooMany2cvs]

BertBert said:

TooMany2cvs said:

Bling visuals apart, lower power draw and - for brake lights - faster response. Indicators may not draw enough for the bulb fail warning to play properly.

All good, I don't have bulb fail warning for the trailer anyway.

Then your towbar wiring is illegal. There must be audible or visible warning of the trailer indicators.

[V8forweekends]

Dr Mike Oxgreen said:

paintman said:

Don't use coloured (LEDs) behind a coloured lens.

Not quite sure what you're saying here, but if you're saying you should use white LEDs behind a coloured lens then that is most definitely incorrect advice.

Unlike a conventional filament bulb which shines a wide mixture of frequencies, a red LED shines all of its power in red-frequency light, nothing else. So if you put it behind a red lens (which lets through only red light) then all the power of the LED goes through the lens, which is exactly what you want.

But roughly speaking, a white LED shines only a third of its power in red-frequency light. The rest is blue and green. If you put that behind a red lens, it'll filter out all the blue and green light and only let through the red light - which is only about a third of the LED's power. Two-thirds of its power has been wasted.

So for tail lights and brake lights you should always buy LEDs that shine red, regardless of whether it's going behind a red lens.

Similarly for indicators you should try to buy LEDs that shine amber, regardless of whether your indicator lens is coloured.

+1 Paintman is 100% wrong on this. LEDs aren't like filament bulbs.

[BertBert]

TooMany2cvs said:

BertBert said:

TooMany2cvs said:

Bling visuals apart, lower power draw and - for brake lights - faster response. Indicators may not draw enough for the bulb fail warning to play properly.

All good, I don't have bulb fail warning for the trailer anyway.

Then your towbar wiring is illegal. There must be audible or visible warning of the trailer indicators.

I thought you meant the clever canbus stuff in the car. The audio is there.

[paintman]

Dr Mike Oxgreen said:

Not quite sure what you're saying here, but if you're saying you should use white LEDs behind a coloured lens then that is most definitely incorrect advice.

Unlike a conventional filament bulb which shines a wide mixture of frequencies, a red LED shines all of its power in red-frequency light, nothing else. So if you put it behind a red lens (which lets through only red light) then all the power of the LED goes through the lens, which is exactly what you want.

But roughly speaking, a white LED shines only a third of its power in red-frequency light. The rest is blue and green. If you put that behind a red lens, it'll filter out all the blue and green light and only let through the red light - which is only about a third of the LED's power. Two-thirds of its power has been wasted.

So for tail lights and brake lights you should always buy LEDs that shine red, regardless of whether it's going behind a red lens.

Similarly for indicators you should try to buy LEDs that shine amber, regardless of whether your indicator lens is coloured.

Edited by Dr Mike Oxgreen on Friday 6th February 14:06

I fitted red ones to the brake/sidelight on the RRC & was frankly disappointed - even my wife commented on the lack of light after following me in her own car! - so much so I went back to conventional bulbs. So based on my own experience.
I should add that this was some years ago, I was given them by a rep & assured they were the best thing since sliced bread. Perhaps things have improved & I'm happy to stand corrected if that's the case. Any recommendations?

Edited by paintman on Friday 6th February 18:38

[Dr Mike Oxgreen]

paintman said:

I fitted red ones to the brake/sidelight on the RRC & was frankly disappointed - even my wife commented on the lack of light after following me in her own car! - so much so I went back to conventional bulbs. So based on my own experience.

But you didn't compare a white LED with a red one - which I did do years ago, to confirm what I kinda knew would be the case. Two LEDs of the same power: one red and one white, installed on each side of my car. The white one gave significantly less light through the red lenses than the red one did. If you'd fitted white ones you'd have been even more disappointed!

LEDs have improved greatly, although to a certain extent the replacement bulbs fitted into "normal" fittings still suffer the same problem: LEDs are very directional, and often fail to illuminate the whole of the reflector properly.

[paintman]

Interesting that they are very directional & don't fully illuminate the fitting. Will stick with conventional bulbs. Presumably the way to go would be to buy complete LED units as in Rambo's link above?
I've got them in torches - including a terralux in a 3-cell Maglite & that made a huge difference over the usual bulb. Guessing that the directional thing is a major factor?

Edited by paintman on Saturday 7th February 10:26

[rambo19]

I have put LED bulbs in my 110 land rover, I had to fit a different relay for the indicators because they flashed to fast.
I used these;
http://www.ebay.co.uk/itm/231376290721?_trksid=p20...

and these;
http://www.ebay.co.uk/itm/390896689219?_trksid=p20...

But, if I was the OP, I would put new LED units on the trailer.