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Look at the photograph below that I took of a surface at Locals, my favorite restaurant in Poolesville, Maryland.  If you were to slide your hand over this surface, would you find it smooth or bumpy? In the photograph below, the white arrow shows the part of the surface that I photographed above.  Yes, those diagonal grooves in the first photograph are nothing more than a pattern of light and dark bands on the floor produced by sunlight shinning through the blinds on a window!  The illusion shown in the first photograph has to do with the way our brain perceives contrast. We associate dark areas with surfaces that are blocked from receiving light (they are in a shadow) and lighter areas with surfaces that are exposed to light. When we see a pattern of alternating light and dark bands, our brains create the perception of relief (a grooved pattern) in the surface that we are looking at, even though it is very smooth. As I have mentioned before, we do not passively perceive the world as it is. Rather, our brain creates a representation of the world based on the information it receives, which is what we perceive. This representation is not veridical, it is fake, but it is correlated to reality, thus it is not false. However, there are many situations, such as the one I described here, where our perception of reality proves to be highly inaccurate. The way we perceive contrast is an active area of research in several scientific disciplines. The photographs belong to the author and can only be used with permission.
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We are so accustomed to seeing light around us that very few people realize that in a very clear environment you will not see a beam of light unless it is aimed at your eyes. The reason we see rays of light, even if they are not aimed at our eyes, is that there are particles in the environment that disperse the light. It is this dispersed light which we see when we see a beam of light not directed at us. Dispersion of light by particles in the environment is a very well-known effect used in entertainment. Theaters and other venues use fog machines that heat a solution of water and glycol producing vapor. The vapor is then expelled through a nozzle where it mixes with the cooler air in the theater to produce a particulate fog, which lingers in the air due to its density and can be fanned around the premises. This vapor will dissipate the light from any ray of light making it visible and creating great special effects. The video below shows a light shining through stage fog at the Signature Theater in Virginia. The video below features a stela found in the Mayan city of Caracol in Belize, which is exhibited at the Penn Museum in Pennsylvania. Mayans used these stones to mark time. This stela, which shows an image of the ruling king, celebrates a date equivalent to May 10, 613 CE. The stone features an elaborate design that includes the ruler, his attire, and portraits of his ancestors. Besides the anthropological and historical significance of the stone, a thing that caught my attention is how the lines in the figure on the stone were traced. The creators of the museum exhibit chose an LCD light projector that traces with white lines the contours of the design of the stone when you press a button and them untraces them after several seconds as is shown in the video. I thought it would be interesting to film the tracing of the design by the projector in slow motion, but I was surprised by the video I obtained which showed the white lines of the stone flickering in a pattern that moved from left to right and that seemed to display occasional flashes of color. When I examined the video frame by frame, I found that the LCD projector did not use white light to create the lines at all. It used an alternating pattern of blue, purple (or red), yellow, and green lines to create the sensation of white lines. This pattern had an apparent left to right movement which maybe has to do with the very fast transition from one color to another.. These types of projectors are quite sophisticated, and if you are interested you can find an explanation of how they work here. The photographs of the stela can only be used with permission of the author. All of us have seen fire burning. Fire emits light of its own, and the colors we associate with fire are colors such as red, yellow, orange, and blue. Additionally, when a regular light beam is directed at a regular fire, it will go right through it, so fire is not an entity that casts a shadow. In the video below, James Orgill from the YouTube Channel The Action Lab manipulates the lighting and the material burning in the fire to produce black fire, a fire that absorbs light and casts a shadow! Most people are amazed by the multicolored fishes that they see in aquariums. Many wonder how such fishes can survive in the wild. After all, aren’t those bright colors on their bodies like a bull’s eye for predators? What must be remembered is that different wavelengths of light are absorbed by water to different extents. The most extreme case is that of red light. In the video below Kendall Roberg shows how colors change the deeper you dive. The video is about selecting the right fishing lure, but it demonstrates that as depth increases, the the color red is perceived as red to a lesser degree (because there is less red light to reflect) until it comes a point when it appears black. Other colors are also affected, but not as much. The reflection of light by the eyes is considered by many painters to be an important detail that can make or break the whole painting in terms of making it look lifelike, and such reflection has been depicted by various painters over the years in many shapes and locations on the pupil and iris of the eyes of the individuals they painted. Below is a sampler that I have put together from my collection of photographs. Painting of Russian Princess Anna Alexandrovna Galitzin by Elisabeth Louise Vigee Le Brun (c. 1797). Baltimore Arts Museum, Baltimore, U.S.A.  Painting of Eunice Brown Fitch, wife of American businessman Timothy Fitch, by Joseph Blackburn (1760). Peabody Essex Museum in Salem, Massachusetts, U.S.A.  Painting of Archduchess Maria Karoline of Austria when she was Princess-Abbess of the Theresian Royal and Imperial Ladies Chapter of the Castle of Prague from 1844 to 1852 (painter unknown). Rosenberg Palace, Prague Castle, Prague, Czech Republic.  Painting of American art collector and Amateur photographer Sarah Lawrence Brooks by John Singer Sargent (1890). The Peabody Essex Museum in Salem, Massachusetts. U.S.A.  But the importance of depicting the reflection of light by the eyes goes beyond art. For some living things it can be a matter of life and death. Many butterflies, moths, and caterpillars have evolved eye spots on their wings or bodies that imitate eyes to deter predators, and these eye patterns also have spots that mimic that twinkle in the eyes!  Butterfly image from pikist is free for use under a public domain license. All other photographs are property of the author and can only be used with permission. What we see with our eyes is visible because light bounces of surfaces in the world around us and then interacts with the receptors in our eyes. In this sense we “see” light all the time. But, much in the same way we can stand next to a train track and watch a train speeding by, can we see a beam of light speeding past us? Until recently this was extremely difficult because light travels incredibly fast (186,282 miles per second). In the video below, the folks from Planet Slow Mo, Gavin and Dan, visited the Compressed Ultrafast Photography (CUP) Laboratory at the California Institute of Technology (Caltech) where researchers are able to film events at speeds up to 10 trillion frames per second. By exploiting the scattering of light as it moves through a medium, the researchers are able to film beams of light as they travel! Check the video below. |
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