I am in psychology class, the light’s are on and I clearly see this black squares on white background. How is this possible? https://www.instructables.com/Optical-Illusion-Black-Squares-and-Gray-Dots/
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I am an engineer and I have worked a lot with projectors. There are 3 ways you could be seeing the black square. I will start with the least likely and work my way up to the most likely.
1. Reflection: It is possible that the black square is a reflection. If there is a pane of glass or a whiteboard that is reflecting the black square (that might be hidden to you) then the reflection might be strong enough to see from where you are. This one is really not likely. Modern projectors do not create a reflection that is strong enough to see from a distance unless you are looking at the surface of the screen.
2. Scatter of the light: Light is never perfectly collimated (meaning that it is a laser that is all going in exactly one direction) so it will scatter a little bit once it hits a surface. That little bit of scatter could be going into your eyes. This is somewhat likely but if you are seeing black squares from further away then the projector is that will decrease the likelihood of this being a cause.
3. You are not seeing the light: This is the most likely cause. Your brain takes in a **lot** of information and processes it. Think about how you can hear your name being called out even though you are in a crowded room having a conversation, or how you can focus on one person’s conversation in a room with a lot of people talking. Your brain filters out the things that you do not want to pay attention to. It filters out most of the things that you are looking at. (For example, how often do you notice what color the outside of the car you are driving is, or the color of the shirt that the cashier is wearing when you go to the grocery store?) When you are watching a movie or a presentation, your brain will likely prioritize the things that you are watching over the objects in the room around you that are not as important. So, while the light from the projector could be hitting the entire wall (and maybe spilling over a little bit further), you are only paying attention to (and therefore are only aware of) the area that the movie (or presentation) is in.
I hope this helps. Let me know if you have any more questions!
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