You can put together a bright and flashy costume with just a few inexpensive supplies and a little time. To keep the focus on the LEDs and their light show, a simple, basic costume design is to build upon a plain black unitard, one with long sleeves. Simply cover the unitard with as many LED rope lights as you desire, placing them in straight or wavy lines.
Buy a comfortable fitting unitard. For these purposes, you might buy one size larger than usual so the fit isn't quite so tight as the addition of rope lights will make movement a little more constricted.
Attach Velcro in loops that fold back and catch on itself all over the unitard. Or use other types of fasteners. You also could sew on small strips of ribbon or cording and tie the rope lights down. Place these fasteners up and down the arms, the legs and across the body of the unitard. Place the fasteners roughly every 3 to 5 inches apart so the LED rope lights won't have a lot of loose places to snag.
Put on the unitard so it'll be stretched out. For the next step, you'll need someone's help.
Have someone thread the rope lights (which will come with their own power source) all over the unitard while you're wearing it. The lights can be threaded so they go up and down the unitard in straight lines or zigzag across the outfit. Make sure there are fasteners to hold the power battery firmly in place as well.
Turn on the power source and your LED costume will light up. Obviously, this sort of costume will stand out better in low lighting settings, such as at dimly lit parties or on a darkened stage against a dark backdrop.
Be careful not to arrange the lights where you'll need to sit. Keep enough of your bottom clear so you can sit without squishing the rope lights. Also avoid getting your costume wet, as that may damage the lights.