It’s been a long time since we’ve talked about how Dark Sky outdoor lighting can be accomplished. Actually, the last time we covered this subject was before LED lighting became the primary landscape lighting product.
Below is taken from the International Dark Sky Association’s Model Light Ordinance (MLO) regarding outdoor residential lighting:
· Outdoor lighting for residential properties including multiple residential properties not having common areas, all outdoor luminaires shall be fully shielded and shall not exceed the allowed lumen output.
· Exceptions:
o At front entry, one unshielded fixture not to exceed 630 lumens or one shielded fixture not to exceed 1260 lumens. The maximum lumen output of unshielded luminaires excluding main entry to be no more than 315 lumens. A shielded fixture does not allow any lighting to be emitted above the horizontal plane of the fixture.
· Low voltage landscape lighting fixtures aimed away from adjacent properties not to exceed 525 lumens each.
· Shielded directional flood lighting aimed so that direct glare is not visible from adjacent properties and not exceeding 1260 lumens. (This most commonly refers to the “security” lights installed at the corners of homes. Bare bulb fixtures are not acceptable here and if they are already in place, install clip-on glare shields. These fixtures should not be aimed above 45 degrees.)
· Lighting installed with a vacancy sensor, where the sensor extinguishes the lights no more than 15 minutes after the area is vacated.
So, according to this document, there are not many restrictions for low voltage landscape lighting except that the fixture should not exceed a lumen output of 525 lumens (approximately a 50 watt halogen lamp) and they should aim away from adjacent properties. There are not any restrictions on total lumens per property or total fixtures. It does not separate up lighting from down lighting or pathway lighting.
The reason that there are very few restrictions on low voltage landscape lighting is simply because it really doesn’t contribute much to sky glow and over all light pollution. The real culprits in light pollution are high voltage, high lumen output fixtures that aim up into the sky, billboard lighting is especially bad in my opinion. This does not mean however that an outdoor lighting designer should not take steps to insure that their design not only follows the Dark Sky MLO but actually improves on it.
Here is what we suggest for developments or property owners who want dark sky outdoor lighting:
It is no longer a good idea to use wattages of lamps to regulate the output of lighting fixtures since a low wattage LED lamp or fixture can produce more lumens than some high wattage halogen lamps. This is why I am specifying everything in lumens, as does the International Dark Sky Association. I agree with them that there is really no need to go above 525 lumens per low voltage landscape lighting fixture, especially in a dark sky friendly development.
It is highly recommended that all outdoor lighting be LED, now that there are so many good options available. The primary benefits of LED lighting are the energy savings, which is a reduction of our global footprint. LED also saves on regular maintenance expenses.
Residential landscape lighting should be shielded and aimed properly to minimize glare. Up lighting should be minimal when used with glare shields placed toward adjacent properties or roadways.
The color of the lighting should be a warm white of 2700K-3000K. When creating a moonlighting effect, the light color should not exceed 4000K (the color of natural moon light).
I recommend that the total lumens of a dark sky outdoor lighting system not exceed 13,125 lumens. Although I cannot find any actual limitations in the MLO, I feel that a dark sky friendly development should have a cap in place. This would be a total of about 25 fixtures at the maximum lumen output. So, if the lighting designer uses fixtures with lower lumen output, they could use more fixtures and still create designs below the 13,125 lumen limit. This would mean that properties that require several shielded pathway fixtures would have no problems meeting these standards while others who may want to really light up some trees would be required to use lower lumen fixtures and fewer of them.
We think that this statement strikes a nice balance to allow the designer to create a great outdoor lighting system on just about any property and still go beyond the Dark Sky MLO. Property owner’s should also bear in mind any additional restrictions applied by the Homeowner’s Association, informing the designer in advance, so that expensive alterations are not necessary after the fact.
Here in the Austin and Texas Hill Country area we are becoming more and more Dark Sky Friendly and more developments are putting restrictions in place. We assisted the city of Horseshoe Bay in developing their dark sky ordinance, and it became the second official Dark-Sky city in Texas. We are very happy to design a beautiful Dark Sky friendly lighting system for your home. Contact us here.
