Glow Sticks are a good comparison. Though they can be as bright or as dim (to the point of not even glowing!) as the player wants them to be keeping in mind that a good majority of the stars are like glow sticks. Dimmer or brighter stars are rarer. If you want something super bright then prepare to have quite the journey ahead of your ICly trying to find and catch a star. The brighter they are, the faster they move, the overall harder they are to catch! Likewise the dimmer they are the slower they move. So dull ones may just 'stand there' suspended in the air or just move really slow.
That is just a general guideline. This is the city of illusion after all. I just want people to have fun with them and create all sorts of neat nicknacks.