As a recommendation, you don't necessarily need high light for CO2 at all. CO2 will increase growth and health in pretty much any lighting situation. It is really the opposite of what you suggest--in high light, you need CO2. In low light you don't, but again, you'll get faster growth and have an easier time with some plants. It can also stave off algae by helping plants grow optimally.
I run low to low-medium light on my small spec v (5g) and still use CO2 for all its beneficial effects. But, that was to achieve the goals I wanted for this tank. What are you wanting to do with the tank that you want CO2? What are your tank dimensions, setup, etc.?