What is BUG rating:
The BUG rating (Backlight, Uplight, and Glare) is a system used to measure how much light from a fixture spills in unwanted directions.
- B (Backlight): Light spilling behind the fixture (can cause light trespass).
- U (Uplight): Light going up into the sky (can contribute to light pollution).
- G (Glare): Light that creates visual discomfort or reduces visibility.
Each category is rated from 0 (best) to 5 (worst) to help designers choose fixtures that minimize light pollution and glare.
The BUG rating (Backlight, Uplight, and Glare) is determined based on IES TM-15-11 and IES TM-11-18 standards, which classify light trespass and skyglow potential. To achieve a zero uplight (U0) rating in a photometric study, follow these steps:
1. Check Fixture Cutoff Classification:
- Look for Full Cutoff or Dark-Sky Compliant fixtures.
- Ensure the fixture has 0% uplight (U0), meaning no light is emitted above 90° from nadir.
2. Analyze BUG Rating in IES Files:
- Obtain the IES file from the manufacturer.
- Load it into AGi32, Dialux, or Photometric Toolbox.
- Identify BUG rating components:
- Backlight (B0-B5) → Light behind the fixture.
- Uplight (U0-U5) → Light above the horizontal plane (Must be U0 for zero uplight).
- Glare (G0-G5) → Light causing glare at high angles.
3. Adjust Mounting Height and Aiming:
- Lower mounting height or use house-side shields to minimize light spill.
- Ensure the fixture is downward-facing (Tilt = 0°).
- Avoid tilted floodlights unless they have strict cutoff optics.
4. Verify Photometric Study Compliance:
- Run the photometric study and verify:
- 0 candela above 90° (U0 requirement).
- Illuminance levels meet local ordinances (e.g., 0.1 fc max at property lines).
- No excessive backlight/glare affecting pedestrians or roadways.
5. Use IDA-Approved Fixtures (If Required):
- If the project requires Dark-Sky Certification, select fixtures from the International Dark-Sky Association (IDA) list.