Football field lights are lights that are used to illuminate a football field. They are typically built at 70 feet high, but may reach up to 250 feet over the pitch in professional stadiums. The lights are usually made of aluminum or steel and are painted red, white, and blue, the national colors of the United States. They are used to mark out playing areas and assist referees and umpires in viewing certain events during matches. The lights are also used by players as they move around the field while talking with teammates or coaches, and sometimes even when they have the ball. The term "football field" is used here to include all forms of athletic fields, such as baseball diamonds, soccer pitches, and indoor arenas where games of footballl are played. Thus, the height of football field lighting systems should be large enough to provide sufficient light over the entire field. Research has shown that professional football teams use about 7500 lumens/square foot when playing at night. This means that their football fields are illuminated to between 10,000 and 20,000 candelas per square meter.