Techniques and Strategies to Imitate the Moon
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.”
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 Purnkinje 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/meters. Monlight has about this same luminance levle. 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 that it illuminates, the most noticeable effect is not only a blueish color but also an absence of all other colors.