There are a bevy of good (some great), detailed, extensive Instructables showing you how to make a near-screen-accurate chest arc reactor for a Iron Man/Tony Stark costume.
I appreciate and enjoy all those but they can be a little time-consuming/expensive/requiring skills you may not have.
So I made this one for under $15 and in under 15 minutes. It's perfect if you need to throw together a costume but don't have a lot of time and/or money (or, in my case, craftsmanship skill).
Here's all you need:1.
A battery-powered, short string of blue LEDs (example: http://www.littlebrightlights.com/site/1435548/product/AC-100B
). My string was Philips brand, 3 feet long (if I remember correctly) with 18 lights but really, any brand and any amount of lights under 20 would probably work just as well -- I got mine at Target for $8. Each of my individual lights are just about 1/2-inch long and 1/8th of an inch across. Try and find lights that are on a string of a shorter length, with as little space between bulbs as possible (this information should be on the box). The lights are the most important thing, not the length of the cord.2.
A hockey puck-shaped piece of white Styrofoam (1-inch thick, just under 3 inches in diameter). I got my piece by cutting the bottom off a conical piece of craft Styrofoam I already had. Packing Styrofoam will probably be too brittle to cut and it also has less opacity/reflectivity. I'd recommend using the lighter, craft Styrofoam that has the crystallized look and is made to be cut (Michaels is a good option).3.
A pen or marker.4.
Tape (glue would work, too). I used 2-inch wide clear packing tape but any kind would probably work.