A few underwater lights have a focusing facility by which the beam angle can be adjusted.

Usually a powerful light suited to the planned activity of the dive, with sufficient power and suitable beam angle.

The beam angle and light output required depend on the objectives of the dive.

Four different beam angles can be obtained on the PAR-64.

The beam angle is determined by the lamp.

Many manufacturers also produce zoom lenses which offer the ability to change the beam angle.

This is no longer necessarily true, so most manufacturers now identify their fixtures by beam angle and light output.

The resulting beam angles for such a system were generally too wide to be used directly for gun laying.

If the beam solid angle is known, then directivity can be calculated as:

The operator marked his screen at each bomb position and changed the beam angle which also recorded time.