I've seen 23W 'daylight' bulbs, they're larger than traditional household incandescents, but if they'll fit they'd probably be quite bright. You might be able to find screw-in bulbs in higher wattages, but they'll probably be fairly large. If the fixture fits standard lightbulbs and a larger CF bulb won't fit, there are 'mini' CF spirals available (similar size as household incandescent bulbs), but I've only seen them in 15W.