Just go to those clearout stores where they always display cheap Energizer batteries among other even cheaper batteries outside, for example ABC store at Bugis and Peninsula, that kind. They will have Philips and Osram and some other funny brands for you to choose from. But they're not very directional, so it depends on how you want to light your tent.
Oh, you can get clamp bulb holders on those stores too, to attach your bulbs to your tent, if you haven't already had a solution to attaching bulbs.
I know that a 100W light bulb can light up a toilet already. I find that those philips energy saving bulb (the one with twisted tube) that rated above 18W already very bright even for my living room...
But to use on light tent will depend on the placement of the light and how many light sources you intend to have (only from the top or lighting from the sides also).
So you might need to play around to see what suited your needs.