We had an aft balcony on Mariner and there was a lot of light for our eyes’ comfort. We have been on other ships where the balcony lights have not been great. You never can predict what you’ll get. If it’s that important to you, I’d suggest bringing a light just in case. FWIW, we have shifted to Kindles instead of books because they have backlights (in addition to several other reasons). Makes it so we don’t have to worry about lighting anymore.