It is a common reaction the world over I suppose: Just as the presenter is ready to begin, someone shouts "could you get the lights, please!" And the room becomes shrouded in darkness, save for the light reflecting off the screen. The presenter? She must be there somewhere, I can hear her speaking (or is the the audience breathing?).
If you want your presentation to be more effective, then don't touch that light switch! Even, when you are using slides, the more lights you can keep on the better off you will be. Remember, we're trying to connect, to tell a story, to sell an idea to the board or other decision makers. It is very difficult to make our pitch if the audience can't see us. The audience is not there to witness the narration of slides, they are there to listen to you and (we hope) become engaged with you and your topic. If the audience can't see you, they will find it difficult to listen, and they are certainly more likely to tune you out.
The audience must experience both your "verbal speech" and your "visual speech." Communication is only about 7% verbal according to an often quoted study. The rest of your message is expressed visually and vocally. Influencing people verbally becomes far more difficult without the other 93%.
Cliff Atkinson reminds us of the empirical evidence which supports the claim that the more the audience can both see you and hear you, the better. Says Cliff, "It turns out that when you watch people speak, the visual cues help you to predict and understand the auditory cues that follow soon after. These visual cues are actually not limited to the lips, but include the entire human face." See Cliff's weblog article "Read My Lips" for more on this.
In corporate meeting rooms across Japan, common practice is to turn all or most of the lights off for presentations. It is also very common for the presenter to sit on the side or back of the table operating the PC while the audience stares at the screen as the "presenter" narrates the slides. This practice is so common that it is considered "normal." It may be normal, but it is not effective at all. Audiences will better understand the presenter's message when they can both see and listen to the presenter. If you think about this, it is quite intuitive, even commonsensical isn't it? Still, it is very good to know there is actual scientific evidence that supports the idea of letting the audience both see you and hear you while giving your talk (with accompanying visual aids such as PowerPoint).
So, to be more effective always make sure that the audience can see you as you as well as hear you.