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.