What do you want to accomplish? Do you need lighting to read? Or just to see the contented faces of your friends and the wine in your glass?
Too much light will kill the atmosphere, creating a light bubble around you and de facto eliminating all your surroundings and dimming the starry skies; but not enough light will prevent you from moving freely on your deck. We may use round deck lights attached to the railing (wire hidden, of course!), or soft moonlighting to create the ambiance without compromising the mood.
You need a real expert able to understand your needs and your goals to give you the exact amount of light you will be comfortable with.
Most importantly, we will listen to you and create a unique design that will let you appreciate fully the flavor of the mise-en-scène.