Light Pollution & Bortle Improvement

See how targeted lighting retrofits translate into darker skies. Enter your current sky brightness, total upward lumens, and planned reductions to estimate the improved sky quality and resulting Bortle class.

Current sky quality meter reading at zenith in mag/arcsec².
Total luminous flux of outdoor fixtures that leak light upward (lumens).
Percentage reduction in lumens after your retrofit or dimming plan.
Estimated percentage of upward light blocked by new shielding or full cut-off fixtures.
Percentage reduction in nightly operating hours from timers, sensors, or curfews.

Examples

  • Switching to shielded LEDs with timers and dimming ⇒ 20.79 mag/arcsec² (Bortle 3)
  • Modest retrofit in a dark suburb with minor shielding ⇒ 21.06 mag/arcsec² (Bortle 3)

FAQ

How accurate is the predicted Bortle class?

It is an estimate based on sky brightness alone. Regional light domes, humidity, or snow cover can shift your perceived class by about ±1 level.

Do motion sensors really help that much?

Yes. Shortening the duty cycle by 30–50% dramatically reduces the integrated lumen-hours spilling upward, especially when paired with shielding.

What if my retrofit includes spectral changes?

Warmer CCT sources and amber LEDs reduce Rayleigh scatter more than this model captures. You can approximate the added benefit by boosting the shielding percentage a few points.

Additional Information

  • Model assumes the mitigations directly scale the upward light contribution; pre-retrofit spill is embedded in the baseline lumens.
  • Shielding and runtime reductions compound with lumen cuts, reflecting how multiple interventions stack together.
  • Results cap at 22 mag/arcsec², roughly the darkest natural night sky measured by SQM devices.
  • Bortle thresholds follow commonly used SQM conversions promoted by IDA and citizen-science campaigns.

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