Dark-Sky Friendly Landscape Lighting in Montana

What does dark-sky friendly lighting mean?

It means outdoor lighting designed to reduce glare, light spilling onto neighbors, and light going up into the sky. DarkSky International publishes five principles for responsible outdoor lighting: lighting should be useful, targeted, low level, controlled and warm-colored. The American Planning Association's knowledgebase summarizes the guide under those same five headings.

The U.S. National Park Service has a very similar list for its own facilities, and it is written plainly enough to use at home: make sure the lighting is necessary, light only where needed, use recessed and fully shielded fixtures, light only when needed, use the minimum light level necessary, and use LEDs in warm colors. The rest of this guide works through what those mean in a yard.

Do I need the light at all?

That is the first question, and the easiest savings. The National Park Service suggests that in many cases reflective tape, paint or reflective surfaces can stand in for a fixture, for example along a driveway edge where people have headlights. Reflective markers at the end of a long rural drive do the job of a pole light without lighting up the hillside.

Walk the property at night before deciding anything. Note where you actually walk and where you trip. Usually it is the steps, the path to the door, and the route to the shop or woodpile. Lighting those well and leaving the rest dark gives a better result than lighting everything. Our landscape lighting design guide makes the same case from a design point of view: contrast is what makes a yard look good at night.

What is a fully shielded fixture?

The National Park Service describes a fully shielded or full cut-off fixture as one that emits light downward onto the task area and not into the sky, with the bulb recessed inside the housing so no part of it is visible at eye level. It warns against globes and diffusers that hang below the fixture, which send a great deal of light upward and cause glare, and says lights directed sideways, such as floodlights, should be avoided.

For a homeowner, the test is simple. Stand at the property line and look at the fixture. If you can see the bright bulb or LED, it is glaring at your neighbors and probably at the sky. Good path lights have a hood or a cap that drops the light onto the ground. Good wall lights point down, with the source hidden. Replacing an old jelly-jar or barn light with a shielded version is often all it takes.

What color temperature should outdoor lights be?

Warm. The National Park Service says 2700 Kelvin can provide excellent color rendition while minimizing unintended impacts, and that for sensitive environments 2200 Kelvin or direct amber options may be appropriate. It explains that LEDs above 2700 Kelvin emit a moderate to significant proportion of blue light, which can create discomfort glare, hurt dark-adapted vision, and may adversely affect human and wildlife health and behavior.

Check the box before you buy, because plenty of LEDs on the shelf run much cooler than that and look bluish and harsh. Warm light also flatters stone, bark and wood, so this is one of the rare cases where the responsible choice and the better-looking choice are the same. Near a creek, a wetland or a wildlife corridor, it is worth looking at the 2200 Kelvin or amber options the Park Service mentions.

Does more light make a property safer?

Not necessarily. The National Park Service says increasing light output does not necessarily make a nighttime environment safer and can often reduce visibility, because glare makes it harder to see what is in the shadows. Anyone who has walked from a bright floodlight into a dark yard knows this. A very bright fixture creates hard shadows right next to it, which is where you least want them.

Motion sensors are a good answer for security. The Park Service lists timers, motion detectors and dimmers as controls that ensure light is used only when needed. A shielded fixture on a motion sensor gives you light when someone is actually there, and a dark yard the rest of the time. Snow also reflects light back up, so a layout that seems restrained in July can glare in January. Plan for the winter level.

What does Missoula's outdoor lighting ordinance require?

The City of Missoula's Building Division says the Missoula Outdoor Lighting Ordinance, Ordinance 3582, went into effect on November 2, 2016, and that new residential building permit applications must include signed copies of an Affirmation of Lighting Ordinance form. The ordinance text (Chapter 8.64 of the municipal code) says a residential light fixture installed after the effective date shall be equipped with full cutoff optics, and that exterior residential lighting may not result in light spillover on adjacent property. It defines a full cutoff fixture as one that emits 0 percent of its light above 90 degrees and 10 percent above 80 degrees from horizontal, and spillover as light that crosses a property line and creates a direct glare source above 0.5 foot-candles at the line.

Older fixtures are generally allowed to stay. The ordinance permits existing nonconforming fixtures without a time limit, with an exception: public complaints about fixtures with unshielded flood lamps rated 880 mean lumens or greater lead to a notice, and the fixture must be replaced or shielded within one year. The City says it looks at existing fixtures on a complaint basis. Pole-mounted residential fixtures are limited to 25 feet or the height of the building, whichever is less. This is a plain reading of the PDF, not legal advice, so confirm details with the Building Division.

Are there lighting rules outside Missoula city limits?

Possibly, and you should ask. We verified the City of Missoula's ordinance, but we did not find a countywide residential lighting rule for Missoula County or Ravalli County that we could confirm, and we are not going to guess. Towns can have their own rules, so check with the planning or building office for your address if you are in or near a town such as Hamilton, Stevensville or Lolo.

Subdivisions are the other place to look. Many have covenants that address exterior lighting, and HOA approval can apply. Our guide on HOA landscape and fence approvals in the Bitterroot covers how to approach that. Even with no rule at all, the neighbor test is a good one: if your light lands in someone else's bedroom window, it is worth fixing.

Can you uplight a tree and still be dark-sky friendly?

It is a trade-off. Uplighting sends light upward by definition, which is what the principles try to limit, and the Missoula residential section we read has no specific carve-out for landscape uplights. Inside city limits, ask the Building Division how the full cutoff rule applies before planning any uplighting. Outside the city, you have more freedom, and it is still worth using it carefully.

If you do light a tree, use the smallest output that shows the bark and lower canopy, keep it warm, aim it into dense foliage rather than past it, and put it on a timer that shuts off at bedtime. Downlighting from within a tree, which our design guide describes, usually gets a similar effect with far less light going skyward, though a tree-mounted fixture needs attention as the tree grows. Our Christmas lights on trees guide covers seasonal displays; Missoula's residential section includes an exception on spillover for seasonal lighting on contiguous property, so read the ordinance text if that applies to you.

How do I make my existing lights dark-sky friendly?

Work through it in order. Remove or switch off anything you do not need. Replace floodlights and exposed-bulb fixtures with shielded versions aimed down. Swap cool lamps for 2700 Kelvin or warmer, and reduce the output where you can. Add a timer, photocell or motion sensor so nothing runs all night by default. Then walk the property line after dark and check for glare.

We design and install low-voltage landscape lighting with shielded fixtures, warm lamps and timers or photocells, and our landscape lighting service starts with deciding what to light and what to leave dark. It is part of our landscaping design work in Missoula and the Bitterroot Valley, and our comparison of low-voltage and solar lighting can help if you are starting from scratch. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call (406) 215-7319 or request a free estimate.

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