Proper illuminance and light direction are critical, as the ball may travel at over 130 miles per hour. In flight, the baseball may be momentarily not visible from direct glare from light sources. Proper pole location and floodlight ensure needed player and spectator visibility. Requirements for the field depend on the type of play — youth sports, high school, college and professional stadiums:

✔ Class I – Facility with OVER 5,000 spectator capacity
✔ Class II – Facility with UNDER 5,000 spectator capacity
✔ Class III – Facility with SOME spectator capacity
✔ Class IV – Facility with NO spectator capacity

✔ Horizontal illuminance – a measure of the lumens per unit area on a horizontal surface. Normally it is measured three feet above the playing surface.
✔ Uniformity illuminance – a measure of the rate of change of illuminance expressed as a ratio between the illuminance level of adjacent measuring points on a uniform grid. The limit of uniformity varies with the speed of the ball.
✔ LUX – a measure of illuminance weighted to the spectral sensitivity of the human eye. It is defined as 1 lux = 1 lumen/square meter.
✔ FC – foot-candle. The official definition is 1 foot-candle = 10.764 lux; however, it is easiest to approximate at 1 foot-candle ≈ 10 lux.