Hello,
A few months ago I've found two Narva Prisma CFLs in the recycle bin (the shape was about like the phlips sl of the third generation). They were magnetically ballasted but the quality was very pour, nothing to do with the philips SL. The bowl was plastic and both lamps have the ballast burned: probably it was undersized, the lamps were 25W but they have a ballast smaller than a philips SL of 25W, the plastic bowl also don't help the heat dissipation.
I think that another member has posted a photo some time ago of a narva prisma. Unfortunaly I dont' have made any photo of the lamps.
...ok I see that you are the guy who have posted the narva prisma
http://www.lighting-gallery.net/gallery/displayimage.php?album=search&cat=0&pos=0&pid=60180My lamps externally was like yours, internally the ballast was on the bottom of the lamp and not between the tubes like in the philips SL. In yours lamps the ballast is also on the bottom?
Another curiosity was the starter that doesn't have any capacitor in parallel to the glowbottle.