Design

Moonlighting: Landscape Lighting Design Imitates Nature

Techniques and Strategies to Imitate the Moon

Author: Steve Parrott

Moonlighting in Landscape Lighting Design

Tree lights project through branches to simulate moonlight. (Design by Ryan Hutchinson.)

COLOR TEMPERATURE

Color temperatures as they relate to landscape lighting design

Figure 1. Color temperatures of various light sources

In all of what we call Nature, the moon stands apart. It is the full moon that ignites our passion for light. It is the full moon that we, as designers, strive to re-create. We sincerely want the homeowner to feel the same feelings that the real moon brings in its romantic fullness.

What is Moonlight?

“I like to think that the moon is there even when I am not looking at it.”
Albert Einstein

We all know what the moon is – a big ball of rocks and dust with craters and a few footprints. But what do we see when we look at the moon? We see sunlight reflecting off its surface. The moon is just a mirror, albeit a very dusty (actually a sparkly crystalline dusty) one. In our attempt to imitate the moon, are we just trying to imitate a dim type of sunlight or does the moon somehow change the light? The answers may surprise you.

1. The Color of the Moon

Sunlight is a mixture of colors that produce what we perceive to be white light. If you bounce sunlight off a reflective white surface, the reflected light will be identical in color to the sunlight. If you bounce sunlight off the surface of a red balloon, the balloon will absorb all colors except red - only red light hits your eye and the balloon appears red.

It turns out that the moon absorbs twice as much violet as it does red. For this reason, the moon is slightly reddish. A full moon when it appears directly overhead has a color temperature of about 4,150°K. Compared to incandescent lighting (around 3,000°K), moonlight is slightly blue but not nearly as blue as a bright sunny day (as much as 10,000°K) (see Figure 1.)

Even though the moon is more red than blue, common belief tells us otherwise. There are songs about the blue moon and filmmakers use blue filters to simulate the moon. Are we deceiving ourselves or do we really perceive moonlight to be blue? Johannes Purkinje knew the answer.

2. The Purkinje Effect (also know as the Purkinje Shift)

Johannes Purkinje, a 19th century physiologist, found that at very low light levels, the human eye could no longer perceive the color red, but could still perceive blues and greens. This occurs because the eye's retinal cones (responsible for color perception) require a lot of light. At lower brightness levels, only the retinal rods are activated. These rods (responsible for seeing fine detail and contrast) can only respond to blues and greens.

The luminance level at which this perceptual shift occurs is at about .001 candelas/meter2. Moonlight has about this same luminance level. This puts moonlight right at the threshold of the Purkinje Shift and this is why the moon appears slightly blue. It should be noted though, that the effect is so slight that the brain easily shifts its perception to judging the moon to be white.

If we shift our gaze from the moon to the ground and other objects it illuminates, the most noticeable effect is not only a bluish color but also an absence of all other colors. The following photo set shows the dramatic difference between colors as perceived by a digital camera and by the eye.

Snow Canyon under moonlight

Snow Canyon under moonlight as seen by the human eye.

This is a photo of Snow Canyon, Utah taken under a full moon at about 2 am. Color temperature was set in the camera at 4,150º K.

This is the same photo color-corrected to represent how I remember the scene to actually appear in my vision. The scotopic light levels removed most color, while the Purkinje Effect made the scene seem bluer than it actually was.

Do we want to imitate the Purkinje Shift in our Landscape Lighting Design?

A minority of designers say 'yes' and put blue filters in all their fixtures. Most others prefer to use unfiltered halogen lamps that more approximate how we see colors during the day. A discussion of this involves how humans perceive color.

3. Color Perception What is the perception of landscape lighting when it is warm (like daylight) or cool (like moonlight)? This is a very essential query. It calls into question whether we are trying to imitate the perception of moonlight or the perception of daytime or interior illumination. I believe the answer is that a combination of perceptions is involved. Most successful lighting projects have areas that are brightly lit, others that are dim or dappled and the remainder that have only ambient illumination. Vision research tells us that people tend to experience warm lighting (such as 3,000o K halogen) to be welcoming, cheerful and bright. Cool (blue) lighting is perceived to be more subdued, mysterious and dim.
	Which do you prefer?
The pictures to the right are meant to simulate this difference. I believe it's safe to say that the warmer scene on the left would better succeed in creating an environment that welcomes a visitor. Slightly-blue lighting does look more moon-like, but overly blue lighting is obviously artificial. Note, however, when people spend time in either warm or cool light, they eventually adapt to the color shift and the light seems neither warm nor cool.	Lighting with 3,000° K (Halogen). (Design by Mike Lenyk.)	Photo retouched to simulate lighting at about 8,000° K (blue filter).
Keep in mind that our light levels using halogen luminaires is about 100 times brighter than moonlight. While we may see dim moonlight as slightly blue, when we are presented with a light 100 times brighter, the blue color may seem artificial.

4. Moonlighting Tools and Mounting Techniques Fixture Type. The CAST Tree Light (CCTL1C) is an MR-16 fixture designed specifically for moonlighting. The extra long shroud along one side allows for additional shielding from glare.This enables the designer to mount the fixture at lower heights without causing visual discomfort to the viewer. The solid bronze knuckle can be adjusted to any angle. Mounting. The CAST Tree Light includes a tri-pronged mounting bracket. A slot in the bracket allows the installer to first install the bracket (with a power drill), then slip and secure the fixture in place. The Tree Mount Stainless Steel Hanger Bolts (CTREEH1) have built-in spacers to provide an air space between bracket and tree preventing the growth of fungus and mold. (Figure 2.)		The CAST Tree Light (CCTL1C)
Figure 2. CAST Tree Mount Stainless Steel Hanger Bolts (CTREEH1) provide an air space between bracket and tree to prevent the growth of tree fungus and mold.		Solid bronze tree mounting bracket included with CAST Tree Light (CCTL1C). Slot allows fixture to be inserted after the bracket has been mounted.

Since leaves are at the tops of palm trees, mounted tree lights are used as a general light wash on the ground, or (as pictured here) to create shadows of neighboring trees. (Design by Steve Middleton.)	Special Case: Moonlighting from Palm Trees Mounting brackets attached to deciduous and evergreen trees will need to be periodically backed off from the bark as the tree circumference grows. Palm trees, on the other hand, do not grow in circumference and the only adjustment needed may be to increase the mounting height. Many palms have extensive woody spikes or bark structures that require extra-long screws to secure brackets. Some even require the use of a mounting ring that encircles the trunk.	Wiring Notes: Various acceptable wire harnesses are available to secure wire leads to trees. The nails or screws in these harnesses should be stainless steel. Wires should be loosely secured to allow for tree growth. Wire harnesses should be periodically inspected and adjusted to prevent bark overgrowth.

5. Heights and Angles

To simulate the light of the moon, we mount fixtures as close to the moon as we can (just kidding). Ideally, we mount fixtures at least 25 ft. high and project the light through lower branches. This illuminates the ground with the kind of dappled light that suggests the moon.

The ideal mounting height is set to minimize potential direct glare while attaining the maximum area of illumination. Direct glare results when light from the bare lamp enters an observer's pupil at a low-enough angle so the bright light projects onto the retina. This angle is estimated to be about 45 degrees (halfway between horizontal and vertical).

Keep in mind that the 45 degree Cone of Comfort (my own term) moves as the viewer's head moves. You may mount a fixture 50 ft. up a tree, but if that tree is above a deck, then someone laying on a lounge chair will be staring directly at it. In setting positions for tree lights, consider where viewers will gaze and position the lights accordingly.

Figure 3. The Cone of Comfort that should remain free of bright light intrusion.

6. Examples

The following photos are examples of effective uses of moonlighting. Notes describe both design and schematic elements. Note, for the purpose of our discussion only the tree lighting parts of the design are discussed - in each case many other fixtures were used.

Moonlighting to add depth to a landscape lighting design

Design: By using moonlighting along a driveway, the designer adds considerable visual interest as well as creating depth. Driving into the property, the viewer becomes a participant in the lighting scene and is led towards the front door by the visual path of illumination. (Design by Glen Kreger.)

Scheme: Two tree lights with 35 watt, 36 degree lamps mounted at about 25 ft. above grade. First fixture is aimed towards the entrance while the second is aimed further down the drive.

Moonlight - an effective technique to add cohesion to a landscape lighting design.

Design: Tree lights were used to cover a broad expanse of walkway, turf and driveway. There is a risk in projecting moonlight so far from the tree since visual angles decrease with distance. In this case, the low angles were acceptable since the tree is far off to the side for drivers coming in and out of the property. The long shadows lend a somewhat mysterious and dramatic note to the nighttime experience. (Design by Ryan Hutchinson.)

Scheme: Two tree lights with 35 watt, 60 degree lamps mounted about 20 ft. off grade. Note that in this and many lighting projects, trees serve the dual purpose of mounting locations for tree lights and as focal points themselves. This striking and unusual tree was up lit by 3 MR-16 Bullets with 35 watt, 36 degree lamps.

Design: The rustic nature of this stepped walkway is enhanced by skillfully directed moonlighting. Designers should be cautious, however, in using moonlighting to illuminate steps and other high risk passage areas - the dappled light can obscure obstacles in the path. (Design by Jason Sponzilli.)

Scheme: One tree light with a 35 watt, 60 degree lamp mounted about 25 ft. above grade.

Design: Moonlighting projected from this tall tree adds considerable visual interest to this wide expanse of pavement. The moonlighting replaced a 500 watt floodlight attached to the garage (off to the left). Needless to say, the homeowners prefer the new lighting design. (Design by Justin Mercer.)

Scheme: Two tree lights with 35 watt, 36 degree lamps mounted about 40 ft. above grade. The installer needed to use a special harness and pulley to be hoisted to the mounting location. Before deciding on such a challenging location, carefully consider the risks vs. the benefits (and don't forget about what it will take to change the lamps!)

Design: Moonlighting is especially striking after a fresh snowfall. The high reflectance of snow greatly increases the perceived brightness and contrast between light and shadow. This same moonlighting may be barely visible on a lawn of dark grass. (Design by Phil Costello.)

Scheme: One tree light with a 20 watt, 36 degree lamp mounted about 15 ft. above grade. The low mounting height was necessary because the only available trees were fairly short.

7. Conclusions

Moonlight evokes certain positive feelings and impressions that we strive to imitate in our landscape lighting designs. But it is not that we try to exactly match the moon's color or brightness. Rather, we set our own rules for placement and projection based on plans that satisfy the various goals of the lighting design.

(Document No. 00071: Created on: 07/31/08 Last modified on: 08/26/09)

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