articles: the light in your eyes (light part 1)

As I mentioned in my previous post, rhythms & routines (an explanation of biological clocks and strategies for maintaining a consistent sleep pattern) light is the main influential factor in regulating circadian rhythms. In other posts I expound upon various types of light and their affects on various biological functions/ bodily systems. For now, we need to understand how our eyes interpret light and what information it gives them to pass along to the brain (See prior posts for a glossary of sections of the brain and regarding pattern recognition).

In another previous post, I outlined electromagnetic fields– waves produced by a vibrating electric charge– which are capable of traveling through a vacuum, such as space. In contrast, mechanical waves need a medium through which to transport their energy, such as air or water water. These exist in a range of frequencies, i.e. along a spectrum from long and low (radio waves followed by radio waves then microwaves– yes, the same that quickly heat your food– and infrared) to short and high (UV followed by x-rays and gamma rays). Most people are familiar with an oscilloscope, a device used to visually display electrical signal voltage; since sound and vibrations can be seen by converting them to voltages, movies/ TV shows– even fancy stereo systems– frequently use oscilloscopes to dramatic effect. 

What we perceive as color is a combination of a psychological and a physiological response to light waves entering the pupil. This light strikes the surface of the retina, which is lined with light- sensing cells, a.k.a. rods and cones. Rods are sensitive to intensity of light, whereas cones are sensitive to wavelengths along the visible light spectrum. Light waves striking these rods and cones triggers a chemical reaction; electrical impulses are sent to the brain.

Humans’ eyes, which have red, green and blue cones are sensitive to a narrow range of frequencies. This visible light spectrum allows us to distinguish between a sequence: red, orange, yellow, green, blue, indigo and violet (red having the lowest and longest waves– the least energy– to violet having the highest and shortest waves– the most energy). The Beyond red is infrared; beyond blue is ultraviolet (UV). Though invisible, they’re both able to be felt: infrared is warming; UV radiation helps the body manufacture Vitamin D but can cause sunburn and photokeratitus (snow blindness).

Most people don’t realize that white light– sunlight– is composed of the full range of wavelengths along the visible spectrum. It doesn’t seem likely since most colors we blend together are in the form of pigments/ dyes in paint, markers and crayons. My elementary school art teacher crafted a detailed color wheel out of cardboard. She attached an electric drill to the center. When it spun, our class expected to see brown or black (such as we had made so many times by mixing paint) but instead– just as she insisted beforehand– all colors blurred together appeared white. 

In my next posts I define red and blue light and discuss applications/ implications of each. 

ADDITIONAL RESOURCES:

American Academy of Opthalmology: how humans see in color

Neuroscience textbook: anatomical distribution of rods and cones

AZ State University: light & optics (infrared and ultraviolet light)

American Museum of Natural History: light, ultraviolet and infrared

United States’ FDA: ultraviolet (UV) radiation

the genetics of normal and defective color vision

Tetrachromacy Project (Newcastle University)

The Human Tetrachromacy Research Collaborative

Could tetrachromats hold the key to early coronavirus detection?

“Tetrachromatic Color Vision” prepared for the Oxford Companion to Consciousness

Genetics Home Reference: Rod-cone Distrophy

prevalence of red-green color vision defects among Muslims in Manipur, India

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