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Does anyone listen to the podcast “Radiolab”??  It’s an NPR production based out of New York City that focuses its immaculately produced episodes on science.  It is insanely interesting and sometimes their broadcasts stick with you and linger on your brain for days.  For me, “Colors” was one such episode.  It fed my curiosity and pushed me to ask further questions about colors.  How/why do we see what we see?  Why do some people see different colors? What do the animals around us see??  Why is the sky blue?

These are some questions that I will address in Boston Mountain Eye Care’s month long blog series on colors.  If you have any questions about colors you would like answered please submit them here.  Let’s discuss some basics about light and color processing in the eye.  Let’s tear apart the rainbow over the next month.  Let’s talk about colors.

The first question we need to answer is “what is light?”  Without light we do not have colors.  What we call “light” is simply the visible spectrum of electromagnetic radiation.  Electromagnetic radiation is energy that has many uses in our day to day lives.  X-rays that provide valuable medical imaging.  Microwaves that heat up last night’s dinner.  Radio waves that transmit your favorite music to your car stereo.  Sunlight is a form of electromagnetic radiation.  So what is the difference between heating up Mac n Cheese and visible light??  The wavelength of the electromagnetic radiation.  Visible light typically corresponds to a wavelengths of 390 to 700 nanometers.  Examples of shorter wavelengths of energy are damaging ultraviolet rays or X-rays.  A common longer wavelength energy is radio waves.  The human eye has narrow and specific range of the electromagnetic spectrum that it will respond to.  So … why?  How does the eye respond to this energy?

Let’s use a common object to explain: When white light from the sun hits a red, Fayetteville Razorback football helmet many of the colors from the spectrum are absorbed based on their wavelength.  Those wavelengths that are not absorbed are reflected off of the helmet.  After that reflected light enters your eye through the cornea, passes the pupil, and emerges inside your eye through the lens it is on a clear path towards your retina.  Your retina is composed of cells that process visual information called cones.  All cones are not the same.  About two thirds of the 6.5 million cones on the average human retina respond most readily to red light.  One third of the cones respond to green light.  Only about 2% of the cones on your retina respond to yellow light.  So when that light that is reflected off of a Razorback Red helmet passes through to your retina, your cones are stimulated to different degrees and the resultant palate tells your brain exactly what color you are seeing.  The fact that the cones respond to varying degrees allows us to see so many different hues and shades of color in our world.  It is estimated that humans can see about 7 million different colors.  Popular visual illusions also take advantage of this and take advantage of the fact that our brains play an integral role in the interpretation of color.  It’s been a heavy blog today, so I’m going to leave you with a couple color vision puzzles below.

Check out our blog next week.  Now that we have the basics of color vision down, we can dig into some fun stuff.  Next week we will talk about why the sky is blue and what someone who is color blind might see.  Have a great week everyone!


Dr. Benjamin Lynch
Boston Mountain Eye Care
350 E Sunbridge Drive | Fayetteville, AR | 72703
479.442.3838 |