High wattage headlights

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Post by DavidRutherford »

400w on main beam?! blimey! that's nearly 30A of lampage...

given a bit of losses here and there, and a fairly inefficient alternator, that's nearly a whole horsepower you're losing on main beam. Does the car go slower when you flick on main beam? :shock:
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Post by tom »

just over half a horsepower. 1HP=745W. Bear in mind that the slightest voltage drop will significantly reduce it. Even so with a 45-55A alternator, The battery is going to come in for a caning, sooner or later...

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Post by jeremy »

There are of course other factors that should be taken into account when producing decent lights for night driving.

One thing to be considered with enormously powerful main beams is the contrast when you dip - Its a bit like turning off all the lights and you find your are almost groping in the dark (which can be fun but not to be recommended at 60 MPH)

Another very important factor is the alignment of the light units. judging from cars I've bought very few headlights are properly aligned and it seems MOT testers are only concerned that they don't dazzle - so don't adjust properly when using the beam tester for the MOT test. proper alignment is worth an enormous increase in lamp power - and after all there's no point in lighting the wrong part of the road very brightly and still not lighting the bit you want to see.

I'm sure tinted windows do nothing at all for night vision and somehow the rather ill defined light pattern from a Lucas 7 inch round sealed beam unit seemed useful for seeing obstructions in the gutter on a country road.

Nostalgia for the sealed beam unit and untinted windscreens - They don't make them like they used to! Thank God!


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Post by sleepy0905 »

I agree about the headlight aim i had a situation where the headlights were pointing a mere few feet in front of the car after the front had been fully rebuilt after a smash, i knew they needed adjusting so took it to the mot I told the guy and asked can you adjust them "no problem" he said anyway collected the car it had passed, night time came only to descover they hadnt even been touched i ended up finding a flat wall and setting them my self, which i now do all the time and they are spot one very time but that comes from the days when testers wernt readily available and it was all done by eye and chalk marks on a flat wall in a dark corner of the workshop.
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Post by jeremy »

I agree Sleepy - always set my own - I use a car park fence, coloured tape and a coat!


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Post by Mike E (uk) »

yeah, I would get a flat battery if I had these on all the time, but for just a few minutes at a time it is no problem.

the old fog light switch activates the spotlights too, so the lighting can be moderated.

I do not notice the loss in power, 1hp after alternator losses is not a lot from a 1.9 petrol engine.

The high power bulbs are really unnecessary if you do the wiring mods and set the alignment right, but

It was a good experiment to see what can be done without resorting to massive Cibie spotlights strapped to the car.

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Post by mat_fenwick »


I have now fitted the 55/100w bulbs, and did some probing around with a meter.

With dipped beams (or original main beams the voltage at the bulb was just over 13V.
With main beam, the voltage at the bulb was about 12.5V.
With engine running, battery voltage was hovering just above 14V and stayed constant regardless of whether lights were on or not.

Not had chance to check them out at night yet but they looked visibly brighter when I just swapped one to compare. Time for some relays though I think!

Incedentally, I do have some small combined fog/spot lights below the front bumper, which are fine when using the fog lights but I think the spot lights are too low to be very useful, and I didn't want to put some extra lamps higher up otherwise I may have been mistaken for a rally car :)

Thanks to all for the advice.