Direct answer
Spill light is calculated at defined points on a property boundary using the fixture photometry, mounting geometry, aiming and the calculation grid. The calculation shows what the design produces at those points. Whether that result is acceptable is determined by the local ordinance and the permitting authority, not by the manufacturer.
Who this is for
Owners, facility managers, municipal planners, homeowners' association boards, and neighbours' representatives who need to understand what a lighting design can demonstrate about light beyond the playing surface — and what it cannot.
Why absolute promises fail
Anyone who tells you a court lighting installation will produce no spill and no glare is describing something that does not exist. Light that leaves a luminaire travels until something stops it. Optical control, shielding, aiming, and mounting geometry reduce light beyond the intended surface. They do not eliminate it, and no calculation can demonstrate zero.
What can be produced, honestly, is a calculated illuminance value at specific named points, together with a description of the optical and aiming measures used to reduce light beyond the surface, and a commitment to evaluate the same named points after installation.
This matters commercially as well as ethically. An absolute promise is unenforceable in the vendor's favour and highly enforceable against them. A named-point calculation with an agreed post-installation evaluation is defensible on both sides.
The two phenomena are different
Spill is illuminance falling where it is not wanted — on a neighbour's property, a road, a garden, a bedroom window. It is measured or calculated as illuminance on a plane at a stated point, either horizontal or vertical.
Glare is a visual sensation caused by luminance in the field of view — the brightness of the light source itself as seen from an observer's position. A property can receive very little spill illuminance and still have a clearly visible bright source in view. Reducing spill does not automatically reduce glare, and vice versa.
Because they are different, they need different evaluation:
• Spill is evaluated at points on a plane, with a stated height and orientation.
• Glare is evaluated from observer positions, in a stated viewing direction, and depends on where a person stands and which way they look.
An evaluation that reports only horizontal illuminance at the property line has not addressed glare at all.
Inputs required before a conclusion can be reached
1. Named evaluation points, chosen by the owner or the authority having jurisdiction — not by the bidder. Specify coordinates or a clear physical description.
2. The plane for each point — horizontal, vertical, or both; and the height above grade. A vertical illuminance value at 1.5 metres facing the court is a different number from a horizontal value at ground level.
3. Observer positions and viewing directions for glare evaluation.
4. Applicable ordinance or covenant limits, with the exact metric each limit uses. Ordinances vary in whether they limit horizontal or vertical illuminance, at what height, and at what boundary.
5. Curfew and operating hours, since some limits apply only after a stated time.
6. Existing conditions — other lighting on or near the site that already contributes to readings at those points.
7. Site geometry — pole locations, heights, fence and screen locations, vegetation, structures.
Without named points and stated planes, no spill claim can be verified and no two proposals can be compared.
What gets evaluated, and how each figure is labelled
Figure | Label | Meaning |
Horizontal illuminance at a named boundary point | Calculated | Software prediction at that point, from the modelled layout. |
Vertical illuminance at a named point and orientation | Calculated | Software prediction; orientation-dependent. |
Glare metric from a stated observer position | Calculated | Software prediction for that position and viewing direction. |
Luminaire intensity at high angles | Reported | From the photometric test report; the physical basis of spill control. |
Shielding, visor, or louvre configuration | Specified | The accessory actually being supplied, by part number. |
Aiming angles per fixture | Specified pre-install, Field-measured after | Documented in the aiming report, then verified on site. |
Mounting height and pole position | Specified pre-install, Field-measured after | Design values, then as-built survey. |
Post-installation illuminance at the same named points | Field-measured | A meter reading with stated instrument, date, and conditions. |
Contribution from other existing lighting | Field-measured | Only separable by measuring with the subject installation off. |
That last row is the one most often missed. If a neighbour's reading includes a streetlight and a car park, the subject installation's contribution cannot be established without a reading taken with the subject installation switched off.
What actually reduces light beyond the surface
• Optical distribution. A luminaire whose photometric distribution places little intensity at high angles produces less spill and less glare from the same position. This is a property of the optic and is visible in the test report.
• Mounting height and position. Higher mounting can allow steeper aiming, which reduces the light escaping at shallow angles. Position relative to the boundary matters as much as height.
• Aiming. The largest controllable variable after the layout is fixed, and the one most likely to drift between design and installation.
• Shielding accessories. Visors, shields, and louvres reduce light in specific directions and typically reduce output on the surface as well. That trade-off should be modelled, not discovered.
• Fencing, screens, and planting. Effective for low-angle light, of limited use against a source visible above them.
• Controls and curfew. Switching or dimming after a stated hour reduces impact for the hours that most affect neighbours. This is often the most effective single measure and the least discussed.
Retrofit versus new construction
On new construction, pole placement can be chosen with the boundary in mind, which is the most powerful spill-control tool available. Use it before reaching for shielding accessories.
On a retrofit, pole positions and heights are fixed, so the available measures are optical selection, aiming, shielding, and controls. If an existing layout places a pole close to a boundary, there is a limit to what fixture selection can achieve, and saying so early is better than promising an outcome that geometry prevents. Where the constraint is structural, a re-aimed and re-optic'd retrofit with a curfew control regime is often a more honest proposal than a claim of dramatic improvement.
What can change the answer
• Moving an evaluation point changes the value; two proposals evaluating different points are not comparable.
• Changing the plane or height at a point changes the value.
• Re-aiming after installation changes both spill and glare.
• Adding shielding reduces spill and usually reduces on-surface illuminance; the layout must be re-run.
• Vegetation growth or removal changes screening over time.
• New adjacent lighting changes what a meter reads at the same point.
• A revised ordinance changes the metric or the limit against which the design is checked.
Verification checklist
1. Evaluation points named by the owner or AHJ, with coordinates or unambiguous physical description.
2. Plane and height stated for each point.
3. Observer positions and viewing directions stated for glare evaluation.
4. Applicable ordinance or covenant limit identified with its exact metric.
5. Curfew and operating-hour requirements identified.
6. Luminaire high-angle intensity reviewed from the photometric test report.
7. Shielding accessories specified by part number and included in the calculation.
8. Aiming documented per fixture, and verified on site after installation.
9. Existing contributing lighting identified before commissioning.
10. Post-installation measurement taken at the same named points, with the subject installation both on and off.
11. Every figure labelled calculated or field-measured.
12. No absolute claim about spill or glare appears anywhere in the proposal, the submittal, or the marketing material.
Duvon's role and limits
Duvon Lighting supplies luminaires and shielding accessories, publishes the photometric data that shows how each optic distributes light, and prepares calculated evaluations at points the owner names.
We do not promise the absence of spill, glare, or light trespass, because no design can demonstrate absence and no calculation can prove it. We do not determine ordinance compliance; that determination belongs to the authority having jurisdiction. Where an owner requires an independent evaluation, it should be performed by a party independent of the supplier.
Next step
Send us the site geometry, the boundary points that matter to you, and any ordinance text that applies. We will return a calculated evaluation at those points and tell you plainly what the optics and geometry can and cannot achieve.