Field Angle

Overview

The Field Angle (often "Feldwinkel" in German) is a photometric parameter that describes the opening angle of the usable light cone of a spotlight. It is defined as the angle between two opposite directions around the beam axis at which the luminous intensity (Candela) has fallen to 10% of the maximum luminous intensity on the beam axis.

Therefore, Field Angle is not a device class or a manufacturer's term, but a measurement from the photometric data sheet of a spotlight. It belongs to the family of "beam spread" specifications, which also includes the more narrowly defined Beam Angle.

Distinction from Beam Angle

Field Angle and Beam Angle describe the same light cone at different intensity thresholds:

The Field Angle is therefore always wider than the Beam Angle of the same spotlight because it is measured at a lower intensity. Both are special cases of the more general term "Beam Spread," which denotes an opening angle at any specified intensity threshold.

Significance on Set

The difference between Field Angle and Beam Angle is an indicator of the light's edge characteristic:

• If both angles are close together, the brightness drops steeply towards the edge – the light cone has a comparatively hard, clearly defined edge.
• If the difference is large, the intensity fades out smoothly and gradually – the edge appears soft and graduated.

For lighting, it is particularly relevant that the Field Angle more realistically depicts the actual illumination width on a surface than the Beam Angle, as the less intensely illuminated edge area still contributes to the visible light field. Those who want to cover a specific area evenly will tend to orient themselves by the Field Angle; those who want to position the bright core (e.g., for a face or a special) will orient themselves by the Beam Angle. The values are found in the manufacturers' photometric data sheets and change for zoom or spot/flood adjustable spotlights (e.g., Fresnel) across the adjustment range.