Flash balm is not supposed to go on under foundation though! According to the fantastic (amazing but true) Clarins rep at my Boots - balm is more like a twice a week mask that you don't wipe off. I don't really understand it tbh.
For under foundation I've had uk.clarins.com/main.cfm?prodID=862flash this]] which is lovely. It brightens the skin if you just want to use a bit of concealer, and makes foundation last much better. Since that ran out I've been using Mac Prep & Prime which feels lovely but have had a couple of spots (only been using for about 4 days) so will have to wait and see.
I think the clarins light thing can be used as an illuminator too, whatever that involves.
I think that's why people don't get on with half of these products - nobody's really sure what they're for. I know I'm not, and lovely Clarins girl at Boots always has gaggles of people wanting her.