Dual filament bulb for P100 headlamp

Anyone know where to get dual filament bulbs compatible with P 100 headlamps on a Jaguar MK IV. Want to get rid of mechanical dippers.

Gust Nelson

Hi Gust,

I’m not sure that there is any point in sourcing a dual filament bulb. Many years ago I adapted the holder to take such a bulb and found that I could focus on one filament or the other but not both. The out of focus filament was useless so I obtained a second solenoid to give double dipping.

As it happens I am now using a double LED with a BA20D base but I have soldered a small brass washer across the the two connections so that both are illuminated together. See: http://www.nostalgiatech.co.uk/LED%20Lighting.htm


I am going down this track of fitting duel filament bulbs to a pair of QK596 headlights as found on SS100s. One of the headlights has a dipping solenoid reflector while the other lamp has a fixed reflector. Most likely from a UK car where the near side lamp went out on high beam. Unfortunately the fixed reflector has no chassis on the rear of the reflector to fix a solenoid to & make it dip & the chances of picking up a reflector & associated parts to make it dip would be slim. Hence the duel filament idea. I have bulb holders that will take duel filament bulbs.

Reading past posts the main problem is the focusing, OK for high beam but not low & visa versa. The main problem seems to be the position of the filaments in the bulbs. The high beam filament is larger & to the fore of the bulb while the dip is smaller & to the rear of the bulb which I guess makes focusing unattainable.

I have some duel filament bulbs that are 35 W X 35 W where the filaments are parallel & equidistant in the bulb. The idea is to have one 35 W filament powered for low beam & both filaments powered for high beam.

One would think if fitted in the reflector with the filaments horizontal then you would be able to focus for both high & low beam - thoughts?

Classic cars, not so sure about current cars, when driving on the left have lights dip to the left on low beam which I think is accomplished by the optics of the headlight glass?

Did QK596 or P100 lamps dip to the left or just down?

My QK596 lamps have U fluted headlight glasses, does this mean they will dip left?

Another question, is the Y bracing holding the Lucas badge in front of the reflector & behind the headlight glass a Y or an inverted Y, I have seen photos of both?

Regards Peter

Hi Peter,

I am one of those who decry the dual filament approach and advocate double dipping reflectors.

When I put my car on the road 28 years ago I initially tried modifying a common dual filament bulb so that it could mounted in my P100s without making changes to the original fittings. Fortunately the original arrangement used the Bosch bulbs with quite large diameter bases and these are clamped in the reflector so that you can move them and lock them in position fore and aft over a good range.

The bulb I used had the filaments mounted with the dip filament in front of the main filament. Using this bulb I could only achieve reasonable focus on one or the other beam but the one not in focus was worse than useless. It is possible that with your dual filament bulb where both filaments are in line vertically that you can achieve useful beams on main and dip but I would strongly advise you to test it without making irreversible changes to your lamps.

I guess another appoach that you could consider is to retain the dipping reflector on one of your lamps and use the dual filament bulb on the other.

I am still using my double dipping reflectors (that I think have a slight bias to the side in dip mode) but am now using LED bulbs.


Here is an update to my last post, I have to correct a mistake where I said that the near side lamp went off on high beam, it should have been the off side lamp went off. After some research I have been able to answer some of my questions.

P100s from a Mk1V & some R170 I have, dip on the horizontal axis while the QKs dip on a 45 degree axis to the horizontal so the dipping beam dips to the near side when dipped while the P100s & R170s just dip down vertically. Thinking about it you would have thought the QK dip idea would be the better one but the QKs are older than the P100s so Lucas must have thought that vertical dipping was better.

Fluted lenses apparently concentrate diverging rays of light into a more parallel beam of light.

With the 45 degree tilting axis of the QKs I was getting confused as to the position of the Y tripod, I have now ascertained that it is a Y & not an inverted Y.

Thank you Peter for your comments. I have taken your advice & manufactured a frame to carry a solenoid & converted the non dipping QK into a dipping one, a lot of work but successful. All I need now is some working solenoids.

Regards Peter

Any pictures or details how the dipping solenoid engages with the pivot or reflector as I have solenoid but no indication where or how the movement pushes or pulls
Also is the solenoid active or ‘ dead’ electrically speaking on high beam or dipped beam? About to re-assemble steering column electrics

Hi Richard,

The solenoid should have a rod with a ball on the end and this pushes on the metal finger/lever arrowed bottom right. I seem to remember I needed to make the rod for one of my lamps.



Mine is electrically dead on high beam.

Thanks- got it now- so missing the rod and the spring to pull the reflector back!

Like Peter I opted to convert both my P100 headlights to (angled) dipping. It would appear both horizontal and angled dipping were available for the P100 as I have seen both types. I concur with Rob that the solenoids are de-energised in the ‘full’ position and energise for dip.
This may be an issue for me as it is very unlikely I will require my headlamps to be on full beam other than a very rare occasion so my concern is the length of time, and associated heat and power drain, the solenoids will be on during night driving.
I guess I’ll find out.

I’m the opposite. In the suburbs here there is so much traffic and street lights that nobody uses high beams. If you do, people flash theirs at you. Occasionally you get somebody forgetting to turn their lights on because they apparently can see well enough without them.
So I angled my P100s downwards a bit and leave them on high and nobody has ever flashed at me as a complaint. The low or dipped setting can only be to dip to the left or straight down, so for a driving-on-the-right country where dipping left would be bad, I set the left one to dip straight down. The right one goes off. Maybe some day if I find another dipping setup I’ll make the right dip too, but right now I’m not worried about it. Plenty of other things to do on the car first.
My left hand driving light is a Bosch and also dips down with a solenoid like the Lucas P100. I don’t know what may be the story behind that light, but it’s kind of fun to play with.

Hi Richard,
Assuming that you lamps are not the early type like Rob’s then the spring is quite small and light. It mounts tangentially between a little arm on the reflector and a hole in the fixed rim.

Anyone tried swopping the lights so drivers side pivots and the kerb side is fixed- don’t like the idea of the driver’s light going off just when you might need it
I have never seen a pivot P100 for sale on the dreaded eBay never mind solenoid and fixings

Hello, can anyone point me in the right direction on the correct assembly of a QK596 as fitted to a SS100 which I assume would be the same as a P100 on a MK1V.

Is there a gasket between the glass lens & outer headlight rim?
Is there a gasket between the back of the glass lens & reflector?
Is there a gasket between the reflector & headlight body?

Are these gaskets cork or rubber & what thickness are they?

Regards Peter

I checked my Mk IV P100s and can confirm these details:

1 - no gasket between rim and glass. There is a drain hole in the bottom of the rim. Some people install a thin gasket here but it does not help the glass to sit flush with the edge of the rim;

2 - definitely a gasket between glass and rim. This is essential to keep the reflector clean not just of water but dust too, and to ensure the glass stands proud of the edge of the rim. I made a ring from standard compressible rectangular section rubber. It would have been cork originally no doubt;

3 - a special ‘O’ ring on the flange of the body to seal to the edge of the rim. This ‘O’ ring has a V shaped section that sits in the groove on the flange. I am sure they are not available anymore but I used a compressible rubber of 3mm diameter (3mm I think);

4 - I have had problems with trying to correctly focus double filament bulbs. When it’s right on one beam, it’s not on the other. I am looking at trying to convert them to their original solenoid dipping function. I think there is some past dialogue on this forum about this.

I hope this helps.


There might be a dual filament bulb that works but I didn’t find one. The dipping solenoids is by far the easiest option. LED lighting is useful for driving at night in stop start conditions.



Thanks Peter L & Peter S from Peter B.

I think I have worked out what is needed in the way of gaskets for the QKs. No gasket between the glass lens & ditto between reflector & headlight body, only a gasket between the back of the lens & reflector. I tried a 6mm EPDM sponge rubber seal which fits but I can’t see how tight it is while a 10mm is a tight fit so more experimentation needed.

On the matter of solenoid dipping & double filament dipping as far as I can see from the wiring diagrams in the workshop manual Mk1Vs were solenoid dipping from 45 - 7 for home & export market & in 48 export market both LH & RH used double filament globes while home market stuck with solenoids. Solenoid lamps used a Lucas globe 60W Lucas part # 60 while double filament globe was 35/35W Phillips # 127926.

Does anyone know how the reflectors changed from solenoid to double filament dipping & whether the Phillips globe was a prefocus one.

Regards Peter

Hi Peter,

I’ve messed around with quite a lot of P100s but they have all been of the type that uses the Bosch B20 single filament bulb rather than the Philips type.

Peter S.

I just noticed an error in my point 2 above. I should have said ‘definitely a gasket between the glass and REFLECTOR…’ I’m sure you picked it up. I try to make sure I have no errors or ambiguities in my posts but I do miss some.

I’m shortly to embark on restoring both headlights on my 1938 25/30 Rolls to the original dipping reflector setup. The lights are R100 but essentially they are the same internally as P100. My LH (nearside) lamp still has the dipping solenoid attached, though it’s not operational. The other headlamp has no solenoid (it goes out on dip) but both lights have dipping reflectors angled to project the beam down and to the left, as correct for RHD. I’ve just acquired an old P100L with the dipping mechanism intact, and have now removed the solenoid, after taking some pictures and making a diagram of wiring connections.
I wonder if someone who has played with these solenoids and got them working could talk me through the process? For instance, should both contacts open when the solenoid operates, or only one? Mine only opens the RH one as you look at it from the plunger end. What amperage should the fuse be? I haven’t connected it up to a 12v source yet to check if the solenoid is functioning.
Any help gratefully received!