Here's a way to put some LED lights on a bike safety vest;
In this case it's a child-size vest, but you can of course do it for any size.
I kept the electric circuit as simple as possible, an order to focus on the LED installation;
Sorry, some intermediate steps (and photos) are missing: I'm writing this instructable about a vest that my girlfriend and me made last year
– a bicycle safety vest;
– LEDs; we used white LEDs for front and red LEDs for the rear of the vest;
– a battery; we used a 3.6 Lithium rechargeable battery sold from a broken portable phone, but you can use any other small-sized battery; for example, 3 AAA size batteries with their support would be fine, and you could use Ni-MH rechargeable batteries as well as alkaline 1
– some resistors; their value depends on the tension of the battery (typically between 3.6 and 4.5 V) and the type of LED used (please see next step for details).
– a small piece of prototype electronic card (you know , the type with plenty of holes spaced 1/10 or inch);
– small electric insulated wire, 2 colors if possible, and the most flexible you can find;
– an electric switch (optional);  – some fabric for the inner lining;
– optional: some Velcro (R) band, also for the inner lining; you could also use some pressure button instead.
– soldering iron;
– scissors for electric wire;
– small pliers to bend the LED's pins;
– optional : a drill with a thin bit, the same diameter than the electric wire;