Chemical lights come in different varieteties. A common use is glow sticks.
Glow-sticks, also called lightsticks and chemlights, have many advantages. They do not use batteries, they generate no heat, are inexpensive, and are reasonably disposable. They are used both as a source of illumination and as markers by soldiers, campers and divers. They are also ideal for situations where flammable material, especially gas, abound, such as in the aftermath of and earthquake.
They are also used in night-time fishing as a lure.
Disadvantages include being and expensive light source for protracted use, and putting out fairly modest amounts of light.
Speciality glow sticks include ultraviolet and infrared.