Association

Dark Skies

07/11/2021
Editor

By Phil Trubey

July 11, 2021

The core of our Milky Way galaxy, as photographed from Lake Cuyamaca near Julian by Kevin Wixom.

Late last year, Julian became California’s second “Dark Sky” community following Borrego Springs, both located in San Diego County. Since the RSF Association has recently been debating, and debating and debating a new lighting regulation, I thought it would be informative to give readers an overview of what these dark sky initiatives mean and how they relate to our community.

County Light Pollution

First, here’s a map of estimated light levels in the surrounding region that was made in 2001 (map taken from here).

Rancho Santa Fe is in the orange tier which is described as “Milky Way no longer visible (rural areas adjacent to suburbs)”, which is about right. We are surrounded by red tier areas described as “Less than 100 of the brightest stars visible (suburban areas)”.

San Diego County Dark Sky Ordinance

San Diego County has an ordinance titled Light Pollution that regulates lighting in all unincorporated areas of San Diego County (ie. everything, including Rancho Santa Fe, that isn’t in a city). The ordinance spells out lighting restrictions for three different regions, or zones, within the County. The most restrictive zone, Zone A, is the region within a 15 mile circular radius around Palomar and Mount Laguna Observatories. Zone C is the relatively newly created “Dark Sky” zone that Borrego Springs and Julian have voluntarily joined. And Zone B is everything else.

The zone C restrictions have been certified by the International Dark Sky Association as being compliant with their lighting restrictions.

Here’s a local map showing these restrictive zones.

County zone A for the observatories and the smaller “Dark Sky” zone C restrictive areas for Julian and Borrego Springs.

For all zones, the County light pollution restrictions have three classes of lighting, the first two deal with commercial and safety lighting, while the last, class III, deals with decorative and landscape lighting, which is what most residents care about since it affects what they are permitted to use.

Zone C, Class III Lighting Restrictions

So let’s look at what it takes to be dark sky compliant for landscape lighting. The following restrictions are taken from the current San Diego County Light Pollution ordinance which gives Julian and Borrego Springs its dark sky designation.

  • Lighting greater than 1,000 lumens must be fully shielded (ie. downcast only).
  • No shielding required for lights less than 1,000 lumens.
  • Maximum 10,000 total lumens per acre.
  • All lights have a color temperature of 3000 K or less.
  • All lights extinguished within 2 hours of sunset.
  • Holiday lighting allowed, provided it is used for no more than 60 days in a 12-month period and is off between the hours of 11:00 p.m. and sunrise.

Two things jumped out at me when I looked at this. First, the ordinance says nothing about uplighting. As long as your light source is less than 1,000 lumens, you’re good to go. Second, a 1,000 lumen per light allowance is generous. A typical high quality landscape LED light will output about 330 lumens, be it a path light or uplight.

The only restriction in this list which runs contrary to current RSF practice is the lights out two hours after sunset requirement, as compared to our current 11 pm lights out County ordinance.

The 10,000 lumens per acre allowance is also generous – that would equate to about 30 landscape lights per acre if you had no other outdoor lighting.

Conclusion

This article was only intended to provide information about what a dark sky policy could look like. A full lighting regulation would take into account more things like light trespass and could be made more or less restrictive than County dark skies policies.

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