The standard Ducati ST headlight for the early bikes has a 55 watt halogen dip beam inside a projector and a 55 watt halogen main beam with a standard reflector. When the headlights are on, switching the main beam on will leave the dip switched on too, it does not change from one to the other but keeps both bulbs alight consuming 110 watts of power. The reason for the projector on the dip (Left side while sitting on the bike) is that there is a shield inside the unit that gives a very clean light cut off and concentrates the light where it will not dazzle other drivers.This photo shows the projector inside the headlight. The problem that I have found with this system is that back of the projector lens gets dirty. In this picture you should be able to see through that lens, but you can’t, it looks foggy and when I remove it I will rub a finger across it to show what I mean. This dirt alone is enough to make a difference between poor and good night time lighting.
The standard projector also only has a fixed cutoff inside so it can only provide a dip beam and no more. If we could move the cutoff out of the way of the light then it could provide dip and main beam from the same 55 watt bulb. The separate 55 watt main beam in the right side of the headlight would then be additional or redundant depending on whether you need a more powerful main beam or want to save the load on the bikes electrical system. For another explanation see Wikipedia, about half way down the page under the heading “Projector”.
The answer is to spend £15 (€19) on a Bi-xenon projector kit from ebay China. It is called a Bi-xenon, but has nothing to do with xenon as that is a bulb technology as is halogen – more about that later.
This is what you get in the kit: Item 1 is the main projector with the solenoid that operates the shutter when power is applied to the lead 4. Item 2 is a plastic shroud to make the projector look nice in a car headlight, something that we cannot see in the ST headlight. Pack 3 contains a silicone gasket and a couple of shaped washers for use should you want to fit the projector inside a reflector headlight that uses a H4 (not the ST) halogen bulb as standard.
How the shutter works:
Here is the projector, the bulb goes in on the right side of the picture and the lens is on the left. The red circle shows the cutoff (shutter) in the down position, so this is in the dip position. The cut off is at the top of the projector as the light is emitted upside down just the same as a camera.
The power from the solenoid will be taken from the supply to the main beam bulb so that when main is selected the cutoff will move.
I have heard that some people would like to fit two of these units into the ST headlight, one on each side, I would not advise this as the main headlight lens on the main beam (right) side is patterned to disperse the light from the standard reflector. If you fit a Bi-xenon projector the resultant light output could cause scattered light on dip beam and dazzle oncoming drivers.
In a future post I will also delve into fitting a HID xenon bulb into this unit, with the ballast mounted outside, this will draw 35 watts but provide about 250% more light. I would never fit a xenon kit into a headlight that did not have a projector due to the amount of dangerous light scatter that it will produce.