GR / UGR / TI glare metrics-choose the correct metric and document viewpoints.
Glare is one of the most common reasons sports lighting projects get rejected-often because the wrong metric was used (or the right metric wasn’t documented). This guide shows how to choose the correct glare metric and build a passable workflow.
Answer: For outdoor stadium lighting, GR is typically the most relevant glare metric; UGR is mainly for indoor spaces, while TI matters when driver safety near roads is part of the acceptance criteria.
The fastest way to avoid disputes is to lock the metric + method in writing, define critical viewpoints, and tie glare control to optics + aiming (not only accessories).
Key takeaway #1: Pick the glare metric based on environment: outdoor sports → GR, indoor halls → UGR, road impact → TI (or road criteria).
Key takeaway #2: Glare control is mostly optics + aiming; shielding is a targeted tool, not a default add-on.
Key takeaway #3: If you can’t explain the metric and assumptions, you can’t defend the result at sign-off.
Use this guide when a tender mentions glare limits but the team is unsure whether the correct metric is GR, UGR, or TI-or when
you need to justify your glare strategy to a consultant during review.
Typical scenarios
Outdoor stadium / pitch: you need a defensible GR approach plus practical glare control methods (optics + aiming + shields).
Indoor arenas: your consultant asks for UGR compliance and surface reflectance assumptions.
Road-adjacent venues: driver glare becomes a safety concern-TI (or similar road criteria) may appear in the tender.
Community-adjacent venues: glare and spill together drive complaints; you need to document viewpoints and curfew conditions.
Key requirements / metrics
This comparison table helps you select the correct glare metric and write it into a tender-ready spec.
Metric
Best fit
What it evaluates
Practical notes
GR Glare Rating
Outdoor sports venues (stadiums, pitches)
Perceived discomfort glare from luminaires in outdoor sports viewing conditions.
Common in European sports tenders and consultant reports. Make sure the method and observer/viewing assumptions are documented.
UGR Unified Glare Rating
Indoor sports halls / arenas
Luminance-based glare evaluation for indoor environments with defined room surfaces and observer positions.
UGR is often misapplied to outdoor projects. If it appears in an outdoor tender, confirm the intended approach in writing.
TI Threshold Increment
Road users / driver safety near venues
Disability glare-how much glare reduces visibility for drivers and road users.
Relevant when sports lighting impacts roads/intersections. Define observer positions and approach directions early.
Definitions
GR (Glare Rating) is commonly used for outdoor sports lighting to describe discomfort glare from visible luminaires in typical viewing directions.
UGR is primarily an indoor metric based on luminance distribution and room geometry.
TI is a road-oriented metric that quantifies disability glare-how glare reduces visibility for drivers.
If your project is an outdoor pitch, don’t default to UGR just because you see it frequently in indoor lighting. Instead, follow the tender language and document the method so the sign-off team can verify it.
Typical target ranges
Most tenders specify a maximum value for glare (e.g., “GR ≤ …” or “UGR ≤ …”). If the tender does not give a number, treat it as a risk:
define a project-specific glare criterion in writing before design freeze.
Outdoor sports (typical): GR is the common reference; supplement with a “critical viewpoints” list (players, stands, cameras, neighbors).
Indoor sports (typical): UGR is common; surface reflectance assumptions must be documented.
Road-adjacent (typical): TI or local road glare rules; define observer positions and approach directions.
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FAQ
Can I use UGR for an outdoor stadium project?
UGR is primarily an indoor glare metric. For outdoor sports venues, tenders more commonly reference GR (glare rating) or other outdoor-oriented criteria. If your tender specifies UGR, confirm the exact method and context with the consultant—then document it in the calculation report.
What is TI and when does it matter?
TI (Threshold Increment) is widely used to assess disability glare for drivers and road users. It becomes relevant when your sports lighting is close to roads, intersections, or airport/transport corridors where driver glare is a safety risk.
How do I reduce glare without lowering average lux?
Use optics that better control high-angle light, optimize aiming angles, increase the number of luminaires at lower intensity per unit (instead of fewer very bright units), and apply shielding accessories only where they actually cut the offending angles.
Do higher poles always reduce glare?
Not always. Higher poles can improve uniformity and reduce extreme aiming angles, but they can also increase high-angle visibility if optics and aiming are not optimized. Treat pole height as part of the overall glare strategy.
Do visors and louvers always help?
They help only when they block the specific problematic viewing angles. If they are used as a generic add-on, they can reduce useful light and create new uniformity issues.
