It depends on the light requirements of the plants you intend to keep. It also depends on how deep your tank is. If you have a deep 40 gallon tank getting 3 watts/gallon and a shallow 40 gallon tank getting 3 watts/gallon, the deeper tank is getting notably less light. I have a shallow tank getting 3.6 watts/gallon 12 hours/day, plant food once a week, no CO2, and I can get away with keeping *most* plants that require "medium" light.
Depending on the depth of your tank, I'd say you're just shy of the "medium" light requirement, but there are SO many factors that determine whether you can successfully keep plants. I'd say start with a one or two plants each in the "low" and "medium" light requirement ranges and see how they do, then go from there. It sounds like you've got enough light to give it a go.