Crosswalk Glows

Last updated on September 16, 2023

Crosswalk Glows: Unveiling the Mysteries of Atmospheric Optics

Have you ever noticed a peculiar glow surrounding the painted stripes on a crosswalk? This optical phenomenon, known as a "crosswalk glow," has fascinated observers for years. In this article, we will delve into the intricacies of crosswalk glows and explore the various factors that contribute to their formation.

Opposition Glows: A Multitude of Causes

Crosswalk glows, also referred to as "opposition glows," can arise in several ways. Let's take a closer look at some of the mechanisms that give rise to this intriguing optical phenomenon:

1. Heiligenschein: When dewdrops form on the surface of a crosswalk, they act as tiny lenses that focus light. This focused light is then transmitted back through the drops, creating a bright glow around the shadow of objects, such as a person's head or a camera.

2. Shadow Hiding: When trees or stones cast shadows on a crosswalk, an interesting effect occurs. When the sun is directly opposite the shadow-casting object, the shadows appear to fall behind the object, obscuring them from view. As a result, the area around the antisolar point (the point directly opposite the sun) appears comparatively brighter, contributing to the crosswalk glow.

3. Coherent Backscatter: This phenomenon occurs due to an interference effect caused by closely packed particles in the atmosphere. Coherent backscatter is partially responsible for the glow observed on Mars and the increased brightness of Mars when it is opposite the sun (in opposition).

4. Retroreflection: Minerals found in rocks and glass beads present in crosswalk paint have retroreflective properties. These materials have the ability to reflect light back toward its source. The presence of retroreflective minerals and beads is likely the primary cause of the crosswalk glow, as it is weaker away from the painted stripes. Additionally, the dryness of the road plays a role in enhancing the retroreflection effect.

The Enigmatic Glory

In addition to the aforementioned causes of crosswalk glows, there is another fascinating phenomenon associated with this optical display - the glory. The glory appears as a series of concentric rings of colors around the shadow of an observer's head. It is caused by the diffraction and interference of light waves when they interact with tiny water droplets or other small particles in the atmosphere.

The glory is a captivating sight to behold, with its vibrant hues and ethereal appearance. It often accompanies crosswalk glows, further enhancing the visual spectacle.

Exploring the Crosswalk Glow: A Visual Feast

To truly appreciate the beauty and complexity of crosswalk glows, it is essential to witness them firsthand. Observing a crosswalk glow allows us to marvel at the interplay of light and atmospheric particles, creating a captivating display that defies our expectations.

Here are a few key points to keep in mind when exploring crosswalk glows:

• Crosswalk glows are most commonly observed when the sun is low on the horizon, such as during sunrise or sunset. The angle of the sunlight plays a crucial role in creating the optimal conditions for these optical phenomena to occur.

• The presence of moisture, whether in the form of dew or recent rainfall, can enhance the intensity of crosswalk glows. Moisture acts as a refractive medium, allowing light to bend and interact with particles more effectively.

• Different materials used in crosswalk paint can produce varying degrees of glow. Retroreflective beads embedded in the paint significantly contribute to the intensity and visibility of the crosswalk glow.

• The viewing angle also affects the visibility of crosswalk glows. Moving closer or farther away from the painted stripes can alter the perceived intensity and overall appearance of the glow.

Unveiling the Wonders of Atmospheric Optics

Crosswalk glows are just one example of the countless marvels found within the realm of atmospheric optics. These optical phenomena remind us of the intricate interplay between light and the particles that make up our atmosphere. By studying and appreciating these phenomena, we gain a deeper understanding of the world around us.

So, the next time you find yourself crossing a street adorned with painted stripes, take a moment to observe the enchanting glow that surrounds them. Allow yourself to be captivated by the mysteries of atmospheric optics and embrace the beauty that lies hidden in plain sight.

Crosswalk Glow ~ An Opposition glow on a crosswalk imaged in Turkey by Aysun Ulger. �Aysun Ulger, shown with permission.

On the crosswalk painted stripes the shadow of Aysun’s head - strictly speaking where the shadow of her camera would be - is surrounded by a bright glow.

‘Opposition glows’ arise in several ways.

Heiligenschein: Dewdrops focus light which is then transmitted back through the drops.

Shadow Hiding: Trees and stones cast shadows. Opposite the sun they appear to fall behind the object casting them. The shadows are hidden and so the area around the antisolar point is comparatively brighter.

Coherent backscatter: An interference effect from closely packed particles. It is partly responsible for this glow on Mars and the brightness of Mars in our skies when opposite the sun (opposition).

Retro reflection: Minerals in rocks and glass beads in paint retro-reflect light. The likely cause of the crosswalk glow because the glow is weaker away from the painted stripes and the road was dry.

And of course there is the glory!

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Reference Atmospheric Optics

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