Beam Spread Visualizer
An interactive, bi-directional calculator to visualize geometric light spread. Calculate beam diameter, exact mounting height, or the optimal beam angle required for your architectural target.
Beam Angle Visualizer
Interactive bi-directional optics calculator
The Trigonometry of Light
Selecting the correct optic is critical in architectural lighting design. A narrow spot (10°) might be perfect for highlighting a sculpture from a double-height ceiling, but the same optic mounted low will create an intensely harsh “hotspot.”
How do you calculate beam diameter? By utilizing point-source optical physics, the projected beam diameter (D) at a given distance (d) is evaluated using the formula: D = 2 × d × tan(θ / 2), where θ is the Full Width at Half Maximum (FWHM) beam angle.
Beam Angle vs. Field Angle
It is vital to understand that a light beam does not stop abruptly at the calculated diameter. The Beam Angle represents the cone where the luminous intensity is 50% or higher of the maximum center-beam intensity. The Field Angle (usually much wider) represents where the intensity drops to 10% cutoff threshold.
In contrast-sensitive environments like galleries, light emitted between 50% and 10% peak intensity generates secondary glare if not mitigated by anti-glare snoots, secondary lenses, or honeycomb louvers. When selecting premium optics, such as those from DGA or FLOS, manufacturers provide precise photometric data detailing both angles.
Professional Disclaimer
This tool calculates the geometric, two-dimensional cross-section of a light beam. It ignores field angle spill and secondary optic scattering. It does not calculate point illuminance (Lux) via the inverse square law. For professional lighting specification, always refer to the manufacturer's official IES files.
Need Exact Optics?
We supply European fixtures featuring interchangeable, high-precision lenses.
- DGA Patented Nano-Lenses
- FLOS Light Shadow Optics
- Optical Zoom Projectors
Frequently Asked Questions
What is the difference between Beam Angle and Field Angle?
The Beam Angle is the point at which the luminous intensity of a light source drops to 50% of its maximum center-beam intensity (Full Width at Half Maximum - FWHM). The Field Angle is wider, representing the point where intensity drops to 10%. Relying solely on beam angle omits field angle spill, which can cause secondary glare.
How do I use this calculator for wall washing?
When washing a wall, you must determine the required Spacing to Height Ratio (SHR). Use this calculator to find the beam diameter at your target surface. Ensure the diameters of adjacent fixtures overlap appropriately to prevent dark “scalloping” effects between the light cones.
Does this calculate center-beam lux?
No. This tool calculates the geometric spread of the light cone based on trigonometry. To calculate point illuminance at nadir, you must apply the Inverse Square Law: E_0 = I_0 / d² (where I_0 represents Center Beam Candlepower).