For easier comparison with other products, we use the following photometric terms as defined in American National Standard E1.9 - 2001, "Reporting Photometric Performance Data for Luminaires Used in Entertainment Lighting."

One-tenth-peak illuminance angle
The angle at which the edge of the field is 10 percent of the maximum (usually center) intensity. This is what we used to call "field" or "beam" angle for wash lights. (For hard-focus fixtures, the beam angle is defined by the focussed edge of the open position.)

One-tenth-peak diameter
The diameter of the field defined by the one-tenth-peak illuminance angle.

One-tenth-peak lumens
The light output within the field defined by the one-tenth-peak illuminance angle. This is what we used to call "total luminous output" for wash lights.

Half-peak
50 percent of the maximum intensity.

Cutoff
3 percent of the maximum intensity.

Total lumen output
The light output within the field defined by the cutoff (3%) illuminance angle. This is what we used to call "total luminous output" for profiles.

The standard may be purchased from ESTA.