Lighting a unit square
Place n unit-brightness point lights in the unit square, where the intensity at any point is the sum of 1/distance² to each light, and maximize the intensity at the darkest point of the square.
Formal definition
- ContainerThe unit square [0, 1]², with lower-left corner at (0, 0) and upper-right corner at (1, 1)
- SubmissionThe n light positions lights, together with a claimed minimum intensity that the verifier can rigorously verify
- ConstraintsAll lights lie inside the square; multiple lights may share a position, in which case their intensities add
- Point intensityP = {p₁,…,pₙ} is the multiset of light positions; each unit-brightness light contributes the inverse square of its distance
- Darkest intensityL(P) is the continuous minimum of the intensity over the entire closed square [0, 1]²
- ObjectiveMaximize L(P) over all valid light configurations P; the submitted intensity must be a lower bound on L(P) that the verifier can rigorously verify
Getting a feel for it
Why it is hard
The darkest point typically occurs at a saddle point between lights or at a corner of the square. Moving lights to brighten one dark spot dims another region. Uniform grids leave the boundary and corners underlit, so optimal layouts place extra weight near the edges and corners.
Known results
Friedman's public table lists the best known configuration and value for each n. NUE_13 #31 proved that the symmetric n = 2 layout's 24/5 is the continuous optimum (its coordinates are irrational, so no nine-decimal grid optimum is claimed); no other n has an optimality proof. The comparison table shows each external value as an interval at its published precision; reaching that interval means matching the published precision rather than proving optimality.
SourceCurrent best solutions by n
Each parameter n is an independently scored sub-problem. Select any card to inspect the current record construction or submit a stronger solution.
Discussion (10) ↓Data and citation
All sub-problems in this family — authoritative scores, proof status, coordinates, and sources — are published at the stable URL below under CC BY 4.0. Because scores update as records fall, please cite the file's generatedAt timestamp.
GET https://minmaxarena.com/data/lights-in-a-square.json
Cite the frozen 2026-10 edition: live records change, whereas a frozen edition stays fixed and reproducible.
GET https://minmaxarena.com/data/editions/2026-10/lights-in-a-square.json
BibTeX (click to copy)
@misc{minmaxarena-lights-in-a-square-2026-10,
title = {{Lighting a unit square} (P51)},
author = {{MinMax Arena}},
year = {2026},
note = {Machine-verified records, 2026-10 edition},
url = {https://minmaxarena.com/data/editions/2026-10/lights-in-a-square.json},
license = {CC BY 4.0}
}Discussion
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