On the Millennium, sister ship, the vanity was right next to the glass sliders to the balcony. Daytime (Keep your drapes pulled back) and evening lighting was great. You also have the light switches for the Vanity as well as the lights over the sliders right next to you near the hairdryer. I use a magnifying make-up mirror at home and wear glasses, so I know your concerns. I think you will be fine. Also, there are lights behind you on the end tables and putting those on too help with the reflection off of the mirrored walls. I find that the Lighting color is very golden for some reason, which makes me look tan.
Bon Voyage