What is the circuit? Lamps in series and on series choke ballast, or what?

They're germicidal low pressure mercury lamps that based on the thermionic discharge. (An arc between the ends of a tungsten filament). This phenomenon can also be seen in fluorescent lamps (Commonly in old T12 fluorescents and in CFLs) when their electrodes preheated.

Must be series since there is only one choke.

Yup, series.
Hey Dave, are these bulbs hard to find? Do you know the hour rating for them?

i've seen these in barbershops to steralize the clippers.

I read somewhere in the internet there was 40 Watts incandescent bulb similar shape as a ballast for the low pressure germicidal lamp!

I have wondered how it lights up when you first start the discharge until it is fully discharged

Yes a 40w incandescent bulb provides the 0.35A current required by the 4w 10v odorout bulbs.

Very cool. I have a Sylvania 4W germicidal. The filament is rated 11.5v @ .35a. I also ran mine on a 15w choke, but since I had only one lamp, I used a variac and slowly turned up the voltage until it was at .35 amp. I ran mine inside of a wine glass to stop the UV.

@rjluna2, it lights up right away, as some of the mercury stays vapor just like fluorescent. You can see the mercury condensation on the bulb just like a fluorescent, and some will evaporate when it heats up.

Oh yeah, don. I had Tube 816 Mercury vapor recifier and did an experiment with the circuit with incandescent light as a load varying the voltage and turing on/off heater cathode resulting the effect of Mercury Vapor ionization rates. I did the experiment on my own in the late 1980's while I was studying in Community College.

How come these were used if you have to wear protection? What were they used for?

I have the modern 3w version.

@streetlight98: These were inside of a box, shinning to the passing by air. The intention was to let the UV and the small amount of generated ozone kill germs and break and react with large molecules of the aromatic substances, so remove the odors from the air.
It was before the rather uncontrolled ozone buildup in such treated areas was considered as a problem, so such method is not used anymore.

Today similar UV radiators are used to sterilize water (slowly flowing through quartz tubing surrounding the UV lamp) - there is no free oxygen, so no danger of the ozone generation.

And the higher power ones are used for industrial curing of plastics, paints or resists in lito processes.