Calculator Inputs
Example data table
| Scenario | Run length | Width | Fixture | Lumens | Target lux | Suggested spacing | Estimated fixtures |
|---|---|---|---|---|---|---|---|
| Front walkway | 40 ft | 6 ft | Path lights | 150 lm | 30 | About 6 to 10 ft | 8 to 10 |
| Patio edge wash | 60 ft | 10 ft | Downlights | 450 lm | 40 | About 0.6 to 0.9 times beam width | 10 to 14 |
| Step lighting | 18 ft | 3 ft | Step lights | 80 lm | 20 | About 3 to 5 ft | 5 to 7 |
Formula used
This calculator combines a lux-based estimate with spacing guidance. First it estimates the total lumens needed over the planning area: Lumens_total = (Target_lux * Area) / (CU * LLF).
Then it estimates fixture count: Fixtures = ceil(Lumens_total / Lumens_per_fixture), split across the selected rows. Finally, it converts count into spacing along the run: Spacing = (Run - 2*Setback) / (Fixtures_per_row - 1).
For beam-based fixtures, beam diameter at the ground is approximated as Beam_diameter = 2 * Height * tan(Beam_angle / 2), helping keep overlap smooth.
How to use this calculator
- Pick a layout and fixture type that matches your garden area.
- Enter run length, width, and a practical end setback.
- Set mounting height and beam angle for downlights or spots.
- Choose lumens and a target lux level for your goal.
- Click Calculate to see spacing, fixture counts, and positions.
- Download CSV or PDF to share with your installer.
Lighting spacing targets by use
Path lighting works best when spacing supports the task. Walkway guidance often lands near 20 to 50 lux, while accent runs can stay lower. This calculator blends a lux target with practical spacing ranges, so you can compare layouts quickly. Use tighter spacing at corners, steps, and gates, then keep steady rhythm across straight sections for consistent visibility and calmer night ambiance overall, everywhere.
Lux, lumens, and coverage math
Illuminance targets translate into lumens using the planning area. The tool estimates lumens_total as target_lux times area, divided by CU and LLF to reflect delivery and loss. Fixture count becomes lumens_total divided by lumens per fixture, rounded up. If you raise the lux goal, counts increase first, then spacing shortens, improving uniformity while adding energy demand, material cost, and installation time.
Beam angle and mounting height effects
Beam angle and mounting height shape coverage more than most people expect. A wider beam at the same height spreads light, but reduces peak brightness. The calculator estimates beam diameter at ground as two times height times tangent of half the beam angle. For downlights and spots, aim for overlapping edges rather than isolated circles. If glare appears, lower lumen output or adjust height and angle for comfort and control.
Row layouts and staggering benefits
Wider paths and patios benefit from multiple rows. Rows distribute light laterally, reducing harsh contrast at edges and keeping the centerline readable. Aligned rows keep symmetry, while staggered rows fill gaps between fixtures and smooth the average lux. Use end setbacks to avoid hotspots at boundaries and to protect plants near entrances. When spacing reaches the rule maximum, add fixtures before increasing brightness drastically for safety.
Power planning and transformer headroom
Power planning prevents dim runs and overloaded supplies. If watts per fixture are known, the tool totals wattage and adds headroom for a safer supply size. When watts are unknown, it estimates from lumens using an efficiency assumption. For low voltage systems, long cable runs can drop voltage; shorten runs, use thicker cable, or feed from both ends. Always confirm local electrical rules and waterproof connections before final installation.
FAQs
What target lux should I use for a garden path?
Many paths feel comfortable around 20 to 50 lux. Use lower targets for accent lighting and higher targets for steps, gates, or uneven surfaces where safer footing matters.
What do CU and LLF change in the results?
They adjust how much light is expected to reach the area over time. Lower values increase required lumens and fixtures, reflecting dirt, aging, optics, and layout losses.
How do I choose a beam angle for downlights or spots?
Start with the manufacturer beam angle. Wider beams cover more area with softer edges, while narrow beams concentrate brightness. Aim for overlap between fixtures to avoid bright circles and dark gaps.
When should I use two or three rows?
Use multiple rows when the lit width is large or when you want smoother brightness across a patio. Staggered rows reduce gaps and can improve perceived uniformity without excessive lumen increases.
Why does end setback matter?
Setback prevents hotspots at the start and end of a run and protects planting edges. It also keeps fixtures away from gates and corners where placement or wiring may be constrained.
Can I export results after changing inputs?
Yes. Calculate once to generate an export set. The CSV and PDF buttons download the most recent calculation, including summary results and a preview list of fixture positions.