How We See Colors

The Journey of Light from it's source to our brain!

Review

In order to fully understand how we see light, we need to make sure we remember a few things we just covered.ABSORPTION is when light enters a medium, but does not exit it. The light stays inside the object. REFLECTION is when light is not fully absorbed into an object and some of it bounces off. VISIBLE LIGHT, or light that we can see, is a form of ELECTROMAGNETIC RADIATION. Each color of visible light (ROYGBIV) all have different FREQUENCIES and WAVELENGTHS.

How we Perceive (another word for see) Colors

The absorption and reflection of light waves by various materials results in human perception of color as follows:


  • Most materials absorb light of some frequencies and reflect the rest.
  • If a material absorbs a certain frequency of light, that frequency will not be reflected, so its color will not be perceived by the observer.
  • If the material does not absorb a certain frequency of light, that frequency will be reflected, so its color will be perceived by the observer.
  • If all colors of light are reflected by a material, it will appear white. If all colors of light are absorbed by a material, it will appear black.


QUESTION: What color does the waterfall in the picture below appear to be? What color is being reflected by the waterfall? What colors are being absorbed?

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What does the color that we see depend on?

The color that we see depends on:

(1) the color of light that is shined on the object

(2) the color of light that is reflected by the object.


For example, if an object reflects red wavelengths and absorbs all others, the object will appear red in color.


QUESTION: Number 1 says that the colors we see depends partly on the color of the light that is shined on an object. What colors of light are shined on an object if the light is coming directly from the sun?

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Color Filters

Color filters allow only certain colors of light to pass/transmit through them; they absorb or reflect all other colors.


For example, a blue filter only transmits blue light.Objects seen through a blue filter will look blue if the objects reflect blue; objects of other colors will appear black because the other color wavelengths are being absorbed by the filter.


QUESTION: Remember when we placed the Red and Blue color filters over the Red numbers on the clock? What happened when we places the Red filter over the clock? What happened when we placed the Blue filter over the clock? How does this relate with what you just learned about color filters?

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Electromagnetic Spectrum

Electromagnetic waves have a wide range of wavelengths. The entire range of wavelengths is called the electromagnetic spectrum.

The relationship between the wavelength and energy of waves in various parts of the electromagnetic spectrum can be shown as follows:

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QUESTION: What colors make up the visible light spectrum? Can we see any colors outside of this with just our eyes?

Visible Light (What We Can See)

Visible light is the range of electromagnetic waves that can be detected by the human eye.

The entire range of visible light is called the visible light spectrum.

The wavelengths of visible light are in the middle range of wavelengths/frequencies of electromagnetic waves.

The longer the wavelength, the lower the energy of the wave is.

The human eye reacts to different energies and frequencies of light so that different colors are seen.

Higher frequencies (shorter wavelengths) are perceived as colors toward the blue-violet range and have higher energy.

Lower frequencies (longer wavelengths) are perceived as colors toward the orange-red range and have lower energy.


QUESTION: Since waves are energy, and wavelength determines ENERGY AND COLOR, that means color is connected to heat as well, because HEAT IS ENERGY TOO. Knowing this, which of these flames do you think is hotter? The torch flame on the right or the match flame on the left?

Infrared Radiation

Infrared radiation is the range of electromagnetic waves with

frequencies lower than red on the visible spectrum, thereby having

longer wavelengths and less energy than red wavelengths.


All objects emit infrared radiation, and hotter objects emit more infrared

radiation than cooler objects.


Heat energy is transmitted by infrared radiation.

When objects absorb infrared radiation, they become warmer.


QUESTION: The baby goats in the picture below are huddled around a lamp that shines with a red light, but also emits Infrared Radiation. What property of Infrared Radiation makes these animals huddle around the lamp? (HINT: They need this to survive)

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Ultraviolet Radiation

Ultraviolet radiation is the range of electromagnetic waves with frequencies higher than violet on the visible spectrum, thereby having shorter wavelengths and more energy than violet wavelengths.


Because of the high energy of ultraviolet radiation, too much exposure is damaging to the eyes and skin.


QUESTION: Ultraviolet radiation is used by dentists to kill germs and whiten teeth. Why would they use Ultraviolet light instead of Infrared light?

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