It was a boring class and my concentration started to drift. I tried to stay awake, staring at anything I could to keep my eyes open – probably not the best idea but during these sleepy moments, I couldn’t think of anything better to do to stay awake. Falling asleep, I looked at the window, on the floor, the ceiling, the projector, the… I saw some lights! Just for a second, I saw a flash of lights. Three vertical lines: red, green, and blue. It happened at some point when I stared at the projector (not directly but at an angle – please don’t hurt your eyes), and I didn’t know how or why, but instead of the usual bright white light that I see, I saw three colors.
I knew why I saw these three colors: The projector emits light in an additive color model, and in it, these three colors, red, green, and blue, are the primary colors that can be combined in varying amounts to produce a gamut of colors. But how did I saw them, and why? That was a mystery to me.
It happened again during another class. Now it’s getting personal! I tried to reproduce it so I could see it whenever I want, but no luck. I stared at the projector from different angles (but never directly!), but it didn’t help. Once in a while, I saw it again, and again, and at some point, I figured it out! It is not about how I look at the projector, or from which angle, but what I do at the same time – and what I did to make it appear was… to move my eyes. Yes, if I look at the projector and move my eyes when my eyes dart somewhere and suddenly I look at the projector for a very short time, I see a flash of red, green, and blue – three vertical lines.
I got it all, I knew the how and when except… except for the why. I asked other people, but no one seemed to notice these colors. I asked it repeatedly, speaking with different people at different times, but no one saw that. I tried to instruct people to see these colors, but it didn’t work. Do I have some superpowers? Hard to believe, but, maybe? No one else that I met could see that. I enjoyed my newly discovered not-so-useful superpowers. Once in a while, I checked out different projectors. During classes, lectures, meetings – I took a glance at the projector, moved my eyes, saw the colors, sort of saying “hello” to this mysterious effect, my little “secret” that only I can see, and focused back on the lecture.
Recently, I decided to take the research to the next level, and I Googled it! What a big surprise it was, and a relief, when I saw that I’m not the only one who sees it, and there is a known physical explanation to this no-longer mysterious effect! I don’t know why I didn’t check it before, but now I also know the answer to the why. The effect is called the “rainbow effect” and it’s also visible as colored shadows in high contrast areas of moving objects.
The effect is caused by the structure of Digital Light Processing (DLP) projectors, and specifically, single-chip projectors. These projectors are built from many microscopically small mirrors laid out in a matrix. Roughly speaking, each micro-mirror represents one pixel (sometimes a bit more). A lamp emits light directed to the mirrors. Each mirror can be in one of two states: Either reflect the light to the screen or hide it from the viewer by reflecting it to a different inner location inside the projector that isn’t exposed to the outer world (called a “heat sink”). Changing this state fast enough, and not only black and white colors will be perceived, but a greyscale.
Greyscale is nice, but what about color? Colors are added by setting a color-wheel between the white lamp and the micro-mirrors. The color wheel is divided into multiple sectors, usually red, green, and blue (sometimes other colors are added as well). The wheel rotates and passes only one of these colors to the mirrors for 1/3 of the time, sequentially. As with greyscale, different amount of reflected light of each color creates a light combination that “fools” our eyes and we perceive it as different colors from a reach color gamut.
Now back to the rainbow effect: when one focus his vision on one spot for long enough, the three projected colors will blend into a single color, but when the eye moves and multiple spots are perceived, then the first spot is visible only when the red light came through, the next spot is looked at when only the green light came through, the third spot is seen only with the blue light, and all the rest of the picture (when the eye finally stops) is blended with the right colors.
For me, noticing this phenomenon, chasing it, learning it with my experiments, and finally finding an explanation, was like conducting my own scientific research.
Many scientific discoveries happened by pure chance, thanks to people who paid attention and chased it long enough to reveal the truth. Some of these discoveries are even related to our own bodies. For example, the fact that our eyes can detect light polarization was discovered only in the 19th century. It happened by mistake (and paying attention) when Haidinger studied minerals under polarized light and perceived a faint yellowish stain or brush that remained when he looked directly at the light without interposing the crystal. We wrote about this extra sense in detail in our article: When a Legend Becomes Reality. About another fascinating discovery, that happened just recently, also related to the human body, we will write in our future article.
Although in this case my finding wasn’t previously unknown, but keep your eyes open, you never know what you may discover.
Featured image by PublicDomainPictures from Pixabay.
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