Reply to Pentaxuser.

Yes the 50% setting is when I move the sliding lever into the middle of the scale. My darkroom is unfortunately shared with my motorcycle. I.E. it's primary function is the garage. On the upside, it is quite large, has a water supply and the DUKA is on a shelf about 8 feet away from the enlarger and the light is reflected off the ceiling so the light levels are quite low.

The colour filter graduation on a LPL Enlarger are scaled in Kodak Units which are significantly different from those used in a Durst Enlarger which has it's own scale. The only other make of enlarger that is different was the Leica V35 which has another scale again different to both.

Oh dear, yes I know that DUKA bulbs are now unobtainable (or I have not been able to find a source of supply), but luckily the unit I have was relatively little used before I bought it so should have a good amount of life left before it expires. I know that used units can be obtained relatively easily for around 60 so I may buy another whilst the going is relatively good.
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But to conserve the life of the sodium bulb, I do use a an Ilford ceiling hung safelight which takes a normal 15watt bulb, of which I have a good supply.

I also use a wall hung lamp with a 100 watt blue coated bulb that gives off a light which is approx that of daylight, but obviously this is only used for inspection to assess colour balance after the print or test has been washed and dried.