The angle at which a fixture still emits 10% of its peak intensity — defines the outer boundary of the usable light cone.
Definition
The Field Angle refers to the beam angle of a spotlight within which the light intensity drops to at least 10% of its maximum value. It is measured from the center of the beam to its outer edge.
Practical Application
The Field Angle determines the light distribution on set:
- Area Illumination: Larger angles (40-60°) for soft, even illumination
- Spotlighting: Smaller angles (5-25°) for directed, hard light
- Distance Calculation: Determines the required spotlight position for the desired illuminated area
- Light Mixing: Overlapping multiple Field Angles for uniform lighting
Technical Details
Important technical characteristics:
- Measured in degrees (°) at 10% light drop compared to Beam Angle (50% drop)
- Dependent on the lens, reflector, and lamp type of the spotlight
- Adjustable on zoom spotlights (e.g., 12-40° on Arri M18)
- Influences light fall-off and shadow softness
Practical Tips
- Calculate the Field Angle in advance during spotlight setup for correct positioning
- Use a spot meter to check actual light distribution
- For zoom spotlights: use the narrowest angle for maximum light output
- Use barn doors or flags for further light shaping
Professional Standards
Standardized specifications enable:
- Precise lighting planning in pre-production
- Reproducible setups for continuity shots
- Efficient communication between the camera and lighting departments
- Calculation of light output and power consumption
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