I had a Wotan Duka 10, but it arrived with a very slightly cracked lamp and so I never got to see it lit. The ballast inside is just an ordinary 40W fluorescent ballast; are you sure it only uses 35 Watts total power?

Measured it at 38 watts, last night. You're right about the 40w ballast, which is pictured in the 3rd pic in this gallery.