Image Credit: Espresso Digest
Light roast coffee doesn't have more caffeine bean to bean. It depends on one’s workflow to brew a cup.
Light roast coffee beans are denser than dark roast, so if a volumetric measure is used to brew a cup of coffee, such as a scoop, light roast coffee will be more in weight than a dark roast in your scoop. Consequently, the resultant cup, (assuming a consistent quantity of brew water) will have slightly more caffeine.