Downlight Spacing Calculator
Generate optimal fixture grid layouts using Spacing to Height Ratios (SHR). Guarantee visual uniformity and eliminate dark zones in architectural lighting design.
Downlight Spacing (SHR)
Calculate optimal grid layouts for strict visual uniformity
Understanding Uniformity (U₀)
In professional lighting design, simply achieving a target Lux level is not enough. You must ensure Illuminance Uniformity (U₀). If fixtures are placed too far apart, the room will suffer from alternating bright pools and dark shadows.
The Grid Logic
Our calculator ensures compliance by determining the absolute maximum distance allowed between fixtures. It then calculates how many rows and columns are needed using the ceiling formulation N = ceil(L / S_max) to cover the room dimensions without ever exceeding this limit.
This forces the actual grid spacing to remain strictly below the maximum allowable threshold, satisfying the overall illuminance uniformity criteria.
Professional Disclaimer
This tool assumes an isotropic luminous intensity distribution (circular beam) and an empty, perfectly rectangular room free of architectural obstructions. It provides an idealized uniform layout. Real-world applications—particularly those involving asymmetric wallwashers—require dual-axis SHR inputs and manual micro-adjustments on M&E site plans to accommodate HVAC ducts or sprinkler heads.
Specify High-Comfort Downlights
Uniformity requires superior optics. Explore our architectural downlight collections.
- DGA Ariel & Saturno
- FLOS Light Shadow
Frequently Asked Questions
What is Spacing to Height Ratio (SHR)?
Spacing to Height Ratio (SHR) is a photometric metric provided by luminaire manufacturers. It indicates the maximum allowable distance between two fixtures relative to their mounting height above the working plane, ensuring that the light cones overlap sufficiently to maintain visual uniformity.
How do I use this to prevent dark spots?
By inputting the Room Dimensions and the Luminaire SHR, the calculator determines the maximum allowable spacing. It then rounds up the number of rows and columns to generate an even grid where the actual spacing is guaranteed to be less than the maximum allowable limit, completely preventing dark spots.
How far should downlights be from the wall?
As a general rule in lighting design, the distance from the wall to the first row of downlights should be between 0.33S and 0.5S (where S is the spacing between downlights). This boundary constraint prevents dark scallops along vertical wall perimeters.