OPOD - Prismatic Doors

Last updated on September 16, 2023

OPOD - Prismatic Doors: A Spectacular Display of Colors

Glass doors have the potential to transform into mesmerizing prismatic displays, casting beautiful spectral colors across the surrounding environment. This phenomenon, known as "Prismatic Doors," occurs due to the interaction of light with the edges of the glass. In this article, we will delve deeper into the intricacies of this optical phenomenon and explore the science behind it.

Upon closer inspection by Måns Hagberg, it was revealed that the glass doors in question had a unique design feature—a 45° bevel approximately 1mm wide on each edge. This seemingly inconspicuous detail played a crucial role in the creation of the vibrant colors observed. Interestingly, when the door was rotated counterclockwise, the colored beam initially swung in the opposite direction, defying intuition.

The key to understanding the colorful display lies in the interaction between light and the small 45° bevels on the door edges. There are two distinct ray paths that can generate a spectrum across the floor.

• Path A: Rays enter the large side of the door and exit through the opposite side bevel.
• Path B: Rays enter through the nearside bevel and exit through the opposite face of the door.

Both ray paths can be likened to passing through a 45° prism, causing the dispersion of light into its constituent colors. To visualize this effect, one can hold a prism and project its spectrum onto a wall. By rotating the prism, one can observe how the spectrum initially moves in one direction and then reverses as the prism reaches the minimum deviation condition.

The phenomenon of Prismatic Doors is not exclusive to glass doors alone. Similar prismatic spectra can be observed in various everyday objects, such as:

• Glass bus shelters
• Fish tanks
• Cut-glass tableware

By paying attention to these objects and their interactions with light, one can appreciate the captivating display of colors that nature has to offer.

In conclusion, Prismatic Doors offer a remarkable spectacle of spectral colors, adding a touch of enchantment to our surroundings. The presence of 45° bevels on the edges of glass doors enables the dispersion of light, creating vivid displays that defy our intuition. This optical phenomenon is not limited to doors alone, as it can also be observed in other objects with similar design features. By embracing the beauty of prismatic spectra, we can gain a deeper appreciation for the wonders of atmospheric optics that surround us.

Prismatic Doors

Måns Hagberg (site) pictured this Swedish display of spectral colours emanating from the edge of a glass door. Image ©M�ns Hagberg

Simple refraction through the 90° prism formed by the edge and side could not produce the colours at the suns position when the image was taken.

Closer investigation by Måns showed that the 10mm thick doors had a 45° bevel ~1mm wide on each edge. Another clue was that when the door was rotated counter clockwise (looking from above the hinge) the coloured beam against intuition swung clockwise at first and then counterclockwise.

The keys to the colours are the small 45° bevels on the door edges. There are two ray paths that could form a spectrum across the floor. Path A - Rays enter the large door side and leave through the opposite side bevel. In Path B rays instead enter the nearside bevel and leave though the opposite door face.

In both cases the path is equivalent to passage through a 45° prism.

Hold a prism so that it projects a spectrum on a wall. Rotate it. The spectrum first moves one way and then another as the prism swings through the minimum deviation condition.

The two ray paths.

Look for prismatic spectra from glass doors, bus shelters, fish tanks and your cut-glass tableware.

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Reference Atmospheric Optics

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