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Upward Light Ratio (ULR) is the percentage of a luminaire’s light emitted above the horizontal in its installed position.
For EPC and government projects, ULR matters because it affects sky glow, glare complaints, and acceptance checks.
In this guide you’ll learn (1) what ULR means, (2) typical limits by environmental zones (E1–E4), (3) how to verify ULR using IES photometric files and DIALux, (4) how to choose the right compliance metric (ULR vs BUG vs Full Cut-off), and (5) a practical checklist to reduce uplight without sacrificing road/court illuminance.
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1) What is ULR (Upward Light Ratio)?
ULR describes how much light goes upwards (above 90°) when a luminaire is installed.
It’s not only a luminaire “spec” — tilt angle and aiming can change the real upward component on site.
Quick definition (acceptance-friendly):
- ULR = Upward luminous flux / Total luminous flux (in the installed position)
- Lower ULR = less uplight and lower sky glow risk (when aiming/tilt are controlled)
ULR vs “no uplight / full cut-off”
- Full cut-off / 0% uplight focuses on preventing light above horizontal.
- A fixture can still create uplight if installed with wrong tilt or incorrect aiming.
Practical EPC note: If your acceptance depends on obtrusive light control, treat ULR as an installation result, not a marketing label.
2) Typical ULR / uplight limits (E1–E4 environmental zones)
Many guidelines use environmental zones:
- E1: dark / rural (strictest)
- E2: low district / residential
- E3: urban area
- E4: city center / bright commercial
Project rule: always follow the tender’s referenced standard (ILP/CIE/local).
If unclear, design conservatively: control near-horizontal angles, avoid unnecessary tilt, and verify with simulation.
ULR vs BUG Rating vs Full Cut-off: What EPC Should Use
In tenders and project discussions, these three terms are often mixed up. They are related, but they are not the same. Use the table below to avoid wrong specifications and acceptance disputes.
Quick comparison (EPC-friendly)
| Term | What it describes | Where it is used most | What it is good for | Common mistake |
|---|---|---|---|---|
| ULR (Upward Light Ratio) | % of luminaire flux emitted above horizontal in the installed position | Outdoor lighting guidelines, obtrusive light control | A clear “uplight” indicator (especially for compliance discussions) | Treating ULR as a fixed luminaire-only value (tilt/aiming can change it) |
| BUG Rating (Backlight / Uplight / Glare) | A 3-part rating that summarizes photometric risk zones | North America / IES-style spec checks | Fast screening for uplight + glare risk | Asking for “BUG = good” without verifying installation aiming and spacing |
| Full Cut-off / 0% Uplight | A luminaire output concept: minimal/no light above 90° | Dark-sky or strict obtrusive-light projects | Strong uplight control when installed correctly | Assuming “full cut-off” automatically guarantees low glare or good uniformity |
What EPC should use (practical rule)
- If the project talks about sky glow / obtrusive light / environmental zones → use ULR as the discussion metric.
- If the project is screening fixtures quickly (uplight + glare risk) → check BUG rating (if available) and confirm the IES file is for the exact model.
- If the project is in dark or sensitive areas (near observatories, rural, residential) → specify full cut-off / 0% uplight plus require a simulation report for the installed aiming.
The acceptance-safe approach (best practice)
No single metric guarantees real-world performance. The safest EPC workflow is:
1) request the exact IES photometric file for the offered luminaire
2) verify tilt + aiming + pole layout in a DIALux report
3) lock aiming angles in installation notes for site commissioning
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3) How to check / calculate ULR in real projects
3.1 Check from photometrics (IES files)
Use the correct IES photometric file for the offered model.
- Look for high-angle intensity (near and above 90°).
- If a supplier provides a “generic IES”, simulation results become unreliable.
You can download the correct IES photometric files as part of an engineering deliverables pack.
3.2 Verify at installation level (DIALux)
DIALux reflects real installation:
- pole height, outreach, spacing
- luminaire tilt
- aiming angles (especially for sports lighting)
For acceptance, always get a DIALux report for verification using the matching IES file.
4) Why uplight happens (even with good luminaires)
1) Tilt angle inherited from old brackets
2) Wrong aiming to “fix dark spots”
3) Optics not designed for cut-off (lens + LED board position)
4) Too-wide beam choice causing spill and uplight
5) Practical checklist to reduce ULR (without losing lux)
Street / roadway lighting
For roadway projects, keep 0° tilt whenever possible and control near-horizontal angles.
- Keep 0° tilt whenever possible
- Control uniformity by distribution + spacing, not by adding tilt
- Verify with DIALux and keep the report in the acceptance pack
If you want the best layout quickly, explore roadway lighting solutions and request a verified design pack.
Sports / area lighting (tennis, football, stadium)
Sports and area lighting often require aiming, so optics and spill control matter.
- Use asymmetric optics + proper aiming
- Add visors/louvers where needed
- Control spill boundaries and document aiming table
- Deliver: DIALux report + aiming table + IES list
For project planning, explore sports & area lighting solutions and validate aiming in DIALux.
6) RFQ / Tender checklist (copy-paste for EPC)
For EPC tenders, request the Engineering Support deliverables pack early to avoid redesign during approval.
Ask the supplier to provide:
- Target illuminance & uniformity
- Pole layout (height, spacing, outreach)
- Luminaire model list + matching IES files
- DIALux/Relux report (PDF)
- Tilt limits + aiming table + commissioning notes
- Warranty + spare parts plan
7) Common mistakes that cause acceptance disputes
- Using non-matching IES files
- Changing aiming on site without updating simulation
- Adding tilt instead of fixing distribution
- No documented deliverables pack for inspection
If you want to reduce disputes, request a verification package before installation (IES + DIALux + aiming notes).
FAQ
What does ULR mean?
ULR is the percentage of light emitted above the horizontal in the luminaire’s installed position.
Can a 0% uplight luminaire still create uplight?
Yes. Tilt and aiming can add upward components. Verify in DIALux with real installation parameters.
How do I reduce uplight quickly?
Use 0° tilt, cut-off optics, correct beam angles, and lock aiming with an acceptance-ready DIALux report.
What should EPC teams request for ULR compliance?
Request the exact luminaire IES file, a DIALux/Relux report, and installation notes (tilt limits + aiming table).
What is BUG rating in lighting?
BUG rating summarizes Backlight, Uplight, and Glare into a simple rating format to screen photometric risks. Use it for quick fixture comparison, but still verify installation tilt/aiming and confirm the IES file matches the offered model.
Does full cut-off mean no glare?
Not always. Full cut-off mainly controls high-angle uplight. Glare can still be high if optics, mounting height, aiming, and uniformity are not handled correctly—so a DIALux verification report remains important.
Next step
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Related Pages
- Solutions — Project-ready configurations for different road and area scenarios
- Engineering Support — DIALux/IES deliverables, BOQ-ready configuration, acceptance documents
- Contact — Share drawings / Google Map link and get support.
