Just a heads up. I saw a 12 volt 13w twisty CFL available at Menards. I've seen them online for kind of a high price plus shipping, but this one is $9. Not cheap, but perhaps useful camping, RV or off grid/power outage. I didn't have enough $$ on me to get one to test, but I will pick one up next time around.
Not sure of brand. Medium screw base, 600 lumens. It think it said 8000 hour life. At 600 lumens, 13 watts, it has a hot ballast or is overstating power draw. I find low voltage fluorescent items to under drive the lamps, so it may not be drawing the power it is rated at. It will be interesting to test it out.
At 13.9 volts it draws 1.1 amps = 15.3 watts
It is slightly brighter than a 120 volt Sylvania mini twist CFL I had although it has some use on it. It is slightly less bright than a standard life, soft white 120 volt 60 watt incandescent. I'd say it equals a 55 watt incan.
At 13.5 volts it was drawing 1 amp = 13.5 watts
I could not test other voltages as my variable supply would not start it because of high starting current.
Color temp is the typical warm white CFL type. Color looked nice without strong green or pink colorations although it is slightly more pinkish than incan.
Polarity is not an issue. works on DC in either polarity. Ballast felt warmer than a 120 volt CFL probably due to the extra 1.5 watts lost in a full wave bridge.
Good review; just don't forget it's 12v dc and accidentally
plug into a regular ac socket...! I've always been bugged by
why they don't use different bases. I've got some really old
photgraphic flash bulbs which also use this base...could cause
quite a stir!
My primary interest is emergency lighting, have tried a regular
CFL with lighter-plug 12dc-120ac inverter, powered by jump-start
battery booster pack (15Ah gell cell). Overall efficiency looks
like at might work out about the same, due to the inverter.
With 11W CFL, measured ~0.95A at 13v (12.4W). I've also
used strings of white Xmas lights as low-level emergency
lighting, not that it's needed very often.