The core reason for giving a live presentation for marketing purposes is to present YOU, not your PowerPoint deck. For training or instruction, yes, what’s on the screen may be most important. But for a standard business presentation, your goal is to create chemistry, convince your audience you can deliver on your promises and clarify questions they may have. All these goals relate to you, not the content of your deck, which they can (and probably did) read before the presentation or, alternatively, after.
So don’t turn out the lights–you’re hiding what you’re selling. Keep your presentation area lighted and follow the tips to come to support your efforts to sell yourself with your audiences.