Plan recessed lighting layout with precise offsets, spacings, and grid. Enter room size, rows, columns; get coordinates and diagram instantly.
a₀ = A/(2r), aᵢ = A/r; b₀ = B/(2c), bᵢ = B/c.
Main fixtures (x,y) = (b₀ + i·bᵢ, a₀ + j·aᵢ). Center fixtures (if on): (k·bᵢ, m·aᵢ).
| # | X (ft) | Y (ft) | Type |
|---|---|---|---|
| — | |||
A Recessed Lighting Calculator helps homeowners, designers, and electricians determine how many downlights to install, how far apart to space them, and whether the total output will achieve the target illuminance for the room’s purpose (ambient, task, or accent). By combining room dimensions, a target light level (foot-candles or lux), fixture lumen output, and a spacing criterion from the product datasheet, it returns the required number of fixtures and a suggested grid layout. Transparent equations reveal how each assumption (mounting height, light-loss factor) impacts results so you can fine-tune for aesthetics and energy efficiency.
The core idea is simple: estimate the total lumens your room needs, then divide by the effective lumens per fixture to get the count. Spacing is guided by the fixture’s spacing criterion (SC), which relates recommended spacing to mounting height. Because real rooms have furniture, reflectances, and obstacles, the calculator also previews wall setbacks and rows/columns to distribute light evenly and reduce scalloping. Assumptions include uniform ceiling height, open ceiling plenum, and typical residential reflectances; commercial photometric layouts may require point-by-point calculations with full IES files.
Area and required lumens: \[ A=L\cdot W \ \ (\text{ft}^2), \qquad \Phi_\text{total}=E_\text{target}\cdot A \ \ (\text{lumens}). \]
Effective lumens per fixture (maintained): \[ \Phi_\text{eff}=\Phi_\text{fixture}\cdot LLF . \]
Number of fixtures: \[ N=\left\lceil \frac{\Phi_\text{total}}{\Phi_\text{eff}} \right\rceil . \]
Mounting height and spacing: \[ MH=H_c-H_w,\quad S\approx \mathrm{SC}\cdot MH ,\quad \text{Wall setback } \approx \frac{S}{2}, \] where \(H_w\) is the workplane height (e.g., \(2.5\ \mathrm{ft}\) for counters; \(0\) for floor-level ambient).
Lux/foot-candle conversion: \[ 1\ \mathrm{fc}=10.764\ \mathrm{lux},\qquad E_{\mathrm{fc}}=\frac{E_{\mathrm{lux}}}{10.764}. \]
\(L=16\,\mathrm{ft},\ W=14\,\mathrm{ft}\Rightarrow A=224\ \text{ft}^2\). Target \(E=15\ \mathrm{fc}\Rightarrow \Phi_\text{total}=3360\ \mathrm{lm}\). Fixture \(=900\ \mathrm{lm}\), \(LLF=0.80\Rightarrow \Phi_\text{eff}=720\ \mathrm{lm}\). \(N=\lceil 3360/720\rceil=5\) downlights. Ceiling \(H_c=8\ \mathrm{ft}\), ambient workplane \(H_w=0\Rightarrow MH=8\). With \(\mathrm{SC}=0.80\), \(S\approx6.4\ \mathrm{ft}\), wall setback \(\approx3.2\ \mathrm{ft}\).
\(L=12,\ W=10\Rightarrow A=120\ \text{ft}^2\). Target \(E=35\ \mathrm{fc}\Rightarrow \Phi_\text{total}=4200\ \mathrm{lm}\). 6″ fixture \(=750\ \mathrm{lm}\), \(LLF=0.80\Rightarrow \Phi_\text{eff}=600\ \mathrm{lm}\). \(N=\lceil 4200/600\rceil=7\). Ceiling \(8.5\ \mathrm{ft}\), workplane \(3.0\ \mathrm{ft}\Rightarrow MH=5.5\). With \(\mathrm{SC}=1.0\), \(S\approx5.5\ \mathrm{ft}\); center rows above counter runs with ~\(S/2\) setback from uppers.
\(L=8,\ W=8\Rightarrow A=64\ \text{ft}^2\). Target \(E=20\ \mathrm{fc}\Rightarrow \Phi_\text{total}=1280\ \mathrm{lm}\). 4–5″ fixture \(=600\ \mathrm{lm}\), \(LLF=0.80\Rightarrow \Phi_\text{eff}=480\ \mathrm{lm}\). \(N=\lceil 1280/480\rceil=3\). With \(H_c=8,\ MH=8,\ \mathrm{SC}=0.90\Rightarrow S\approx7.2\ \mathrm{ft}\) (use 2×2 grid symmetry; add vanity task lighting separately).
Use lumens, not “one per X ft².” Compute \(\Phi_\text{total}=E\cdot A\) and divide by \(\Phi_\text{eff}\) per fixture.
A manufacturer value linking recommended spacing to mounting height: \(S\approx \mathrm{SC}\cdot MH\).
Ambient 10–20 fc, kitchen task 30–50 fc, bathroom 20–30 fc. Adjust for preference and reflectance.
Yes, but be mindful of glare and uniformity—more lower-lumen fixtures often look better than few bright ones.
Start at about \(S/2\) from walls to reduce scalloping; tweak for artwork and cabinetry.
4″ offers tighter beams and modern look; 6″ spreads wider. Choose by ceiling height, beam angle, and output.
2700–3000K for cozy living areas, 3000–3500K for kitchens/baths; CRI 90+ for accurate color rendering.
Dimmers add flexibility and save energy. Verify dimmer/driver compatibility with your LED fixtures.
Attics/insulation require IC-rated housings; showers need wet-location trims—always follow local code.
Yes—layer ambient (recessed) with task (undercabinet) and accent (pendants) for best results.