What Is Color? | Physics in Motion

Summary

This segment of 'Physics in Motion' delves into the science of color, explaining how objects absorb and reflect light to produce the visible spectrum. It distinguishes between the primary colors of pigments and light, and demonstrates how mixing these can create white light. The video also explores the concepts of additive and subtractive color mixing, the role of chlorophyll in plant photosynthesis, and how our eyes perceive color through rods and cones. It highlights the importance of color in nature for signaling and disguise, and its enhancement of our visual world.

Takeaways

• 🌈 Color is a part of the electromagnetic spectrum that we can see, known as the visible spectrum.
• 🎨 Objects appear colored because they absorb some wavelengths of light and reflect others that we perceive.
• 🔍 The visible spectrum ranges from violet to red, with each color having a specific wavelength.
• 🚫 Infrared is just beyond the red end of the visible spectrum, and ultraviolet is beyond violet.
• 👀 Human eyes can perceive wavelengths from approximately 390 to 790 nanometers.
• 🌟 It's estimated that humans can distinguish between 18 decillion colors.
• 🟥 The primary colors of light are red, green, and blue, which combine to form white light.
• 🌿 Leaves appear green because they reflect green light and absorb other colors, facilitated by chlorophyll.
• 🖼️ Additive color mixing involves combining light wavelengths to create various colors, including white when all primary colors are combined.
• 🖌️ Subtractive color mixing occurs with pigments or dyes, where some wavelengths are absorbed and others reflected, creating color.
• 👁️‍🗨️ Our eyes contain rods and cones that detect light and color, with cones being responsible for color perception.

Q & A

What is color in the context of the electromagnetic spectrum?

Color is the part of the electromagnetic spectrum that we can see, known as the visible spectrum.

How do objects appear to have different colors?

Objects appear to have different colors because they absorb some wavelengths of light and reflect others. The colors we see are those wavelengths that are not absorbed and are reflected back to our eyes.

What is the range of wavelengths that correspond to the colors we can see?

The spectrum of color ranges from violet to red, with each color having a specific wavelength. Red has the longest wavelength and violet the shortest.

What is the approximate range of wavelengths that human sight can perceive?

Human sight can perceive wavelengths from about 390 to 790 nanometers.

How many colors are estimated to exist in the universe that we can distinguish?

It's been estimated that we can distinguish between 18 decillion colors.

What are the primary colors of light, and what happens when they are mixed?

The primary colors of light are red, green, and blue. When mixed in equal intensities, they produce white light.

What is the difference between the primary colors of pigments and the primary colors of light?

The primary colors of pigments are red, blue, and yellow, while the primary colors of light are red, green, and blue. This difference is due to how pigments absorb and reflect light differently than how light itself combines.

Why does a leaf appear green?

A leaf appears green because it reflects the wavelength of green light and absorbs all the other colors. This is due to the presence of chlorophyll, which is involved in photosynthesis.

What is luminance and how is it measured?

Luminance is the measure of brightness of a surface, measured in candelas per square meter. It is the amount of light reflected off a surface.

How is the color white light produced through additive color mixing?

White light is produced through additive color mixing when the primary colors of light (red, green, and blue) are overlapped in equal intensities.

What is the difference between additive and subtractive color mixing?

Additive color mixing involves combining light of different wavelengths to create colors, while subtractive color mixing involves pigments or dyes that absorb certain wavelengths and reflect others, creating colors by subtraction.

How do our eyes perceive color?

Our eyes perceive color through rods and cones, which are photoreceptor nerve cells. Cones are responsible for color perception, while rods are more sensitive to light but not to color.

Outlines

00:00

🌈 Understanding Color and Light

This segment of 'Physics in Motion' explores the science behind color and light. It begins at All Saints' Church in Atlanta, highlighting the absence of visible light and its role in creating color. Color is explained as part of the electromagnetic spectrum known as the visible spectrum, which we perceive due to the wavelengths of light that objects reflect rather than absorb. The visible spectrum ranges from violet to red, with each color having a specific wavelength. The human eye can perceive wavelengths from approximately 390 to 790 nanometers. The video introduces the concept of primary colors of light—red, green, and blue—and how their combination creates white light, as discovered by Isaac Newton. It also contrasts this with pigment primary colors—red, blue, and yellow—and explains that black is the absence of light. The segment further discusses the properties of light, such as refraction leading to the creation of a spectrum, and the different behaviors of light when passing through materials, resulting in transparency, translucency, or opacity. The concept of luminance is introduced as a measure of brightness, with a distinction made between lumens and watts. The segment concludes with an outdoor demonstration of how leaves appear green due to the reflection of green light and absorption of other wavelengths, a process facilitated by chlorophyll.

05:03

🎨 Exploring Color Mixing and Perception

The second paragraph delves into the principles of color mixing, both additive and subtractive. Additive color mixing is demonstrated using a color projector, where combining red, green, and blue light in equal intensities produces white light. Secondary colors of light—yellow, magenta, and cyan—are created by overlapping two primary colors. The concept of complementary colors, which produce white light when combined, is also discussed, with examples such as green and magenta, blue and yellow, and red and cyan. Subtractive color mixing is introduced as the process by which pigments and dyes reflect and absorb light, leading to the colors we see. The difference between pigments, which are insoluble and derived from inorganic sources, and dyes, which are soluble and often derived from natural sources, is explained. The video then explains how our eyes perceive color through rods and cones, the photoreceptor cells that absorb light and transmit electrical impulses to the brain. The role of nature in using color for various purposes, such as attraction, repulsion, and camouflage, is briefly touched upon before concluding the segment with a reference to the 'Physics in Motion' toolkit for further learning resources.

Keywords

💡Electromagnetic Spectrum

The electromagnetic spectrum refers to the range of all possible frequencies of electromagnetic radiation, from the lowest frequencies (longest wavelengths) to the highest frequencies (shortest wavelengths). In the context of the video, it is the foundation for understanding color, as the visible spectrum is a part of it. The script mentions that the visible spectrum is what makes objects appear in color to our eyes, and it ranges from violet to red wavelengths.

💡Visible Spectrum

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. It is a key concept in the video, as it directly relates to the perception of color. The video explains that objects absorb certain wavelengths and reflect others, which are the colors we see. The visible spectrum is bounded by violet at the shortest wavelength and red at the longest.

💡Wavelength

Wavelength is a measure of the distance between two identical points in a wave, such as the distance between two consecutive crests. In the video, the concept of wavelength is crucial for understanding color, as different colors correspond to different wavelengths within the visible spectrum. The script provides examples, stating that red light has the longest wavelength and violet the shortest.

💡Color

Color is the visual perception of the properties of light that are perceived as varying according to the wavelength of the light. The video delves into the science behind color, explaining that it is a result of the wavelengths of light that are reflected by objects and then detected by our eyes. The script mentions that human sight can perceive a vast number of colors, estimated at 18 decillion.

💡Primary Colors of Light

The primary colors of light are red, green, and blue. These colors are fundamental in the sense that they can be combined in various ways to produce a wide range of other colors. The video explains that when these primary colors are mixed together in equal intensities, they create white light, which is the combination of all colors in the visible spectrum.

💡White Light

White light is a combination of all the colors of the visible light spectrum. The video clarifies that white light is not a color itself but rather the presence of all colors. This is demonstrated when the primary colors of light (red, green, and blue) are mixed together, resulting in white light, as explained by Isaac Newton.

💡Chlorophyll

Chlorophyll is a green pigment found in plants that plays a crucial role in photosynthesis. The video uses chlorophyll as an example of how plants reflect green light and absorb other colors, giving leaves their characteristic green appearance. Chlorophyll is a light-trapping pigment that is most efficient at absorbing red light, which is important for converting light into glucose.

💡Luminance

Luminance is a measure of the perceived brightness of a surface, defined as the amount of light reflected off a surface. The video discusses luminance in the context of how light reflects off a painting, making it appear brighter when illuminated. Luminance is measured in candelas per square meter, and it decreases with the square of the distance from the light source.

💡Additive Color Mixing

Additive color mixing is a process where different colors of light are combined to create new colors. The video explains that by overlapping wavelengths from different parts of the visible spectrum, a wide range of colors can be produced. This is demonstrated when the primary colors of light (red, green, and blue) are mixed to create white light or other colors.

💡Subtractive Color Mixing

Subtractive color mixing is the process by which colors are created by reflecting and absorbing light, typically through pigments or dyes. Unlike additive mixing with light, subtractive mixing involves materials that absorb certain wavelengths, reflecting the rest. The video contrasts this with additive color mixing, explaining that mixing pigments can result in colors that absorb so much light they appear almost black.

💡Rods and Cones

Rods and cones are photoreceptor cells in the retina that allow us to perceive light and color. The video explains that rods are more sensitive to light but do not perceive color, while cones are responsible for color vision. There are many more rods than cones in the human eye, and they contain molecules that absorb light, allowing us to see the colorful world around us.

Highlights

Color is the visible part of the electromagnetic spectrum.

Objects absorb some wavelengths of light and reflect others, which we perceive as color.

The visible spectrum ranges from violet to red, each with a specific wavelength.

Human sight perceives wavelengths from about 390 to 790 nanometers.

It's estimated that humans can distinguish between 18 decillion colors.

Primary colors of pigments are red, blue, and yellow, different from the primary colors of light.

The primary colors of light are red, green, and blue, which combine to form white light.

Isaac Newton discovered that white light is composed of a combination of wavelengths from the visible spectrum.

White light is not a color but the presence of all colors of visible light.

Black is perceived as the absence of light.

Chlorophyll in plants absorbs red light, which is most effective for photosynthesis.

The red edge of the spectrum is where photosynthesis in plants is most active.

Additive color mixing creates an array of colors by overlapping wavelengths from the visible spectrum.

Complementary colors, when combined, produce white light in additive color mixing.

Subtractive color mixing occurs with pigments or dyes, where some wavelengths are absorbed and others reflected.

Mixing too many pigments can result in a color close to black due to absorption of all wavelengths.

Pigments are inorganic and change the color of reflected or transmitted light through selective absorption.

Dyes are biological and dissolve in a medium to transmit color to materials.

The human eye perceives light with rods and cones, which are photoreceptor nerve cells.

Rods are more sensitive to light but not to color, while cones perceive color.

Color serves as a signal in nature for attraction, repulsion, and camouflage.

Transcripts

I'm inside the impressive All Saints' Church,

in Atlanta, but something's missing.

It's the part of the electromagnetic spectrum

that we can see.

The part that makes this... look like this.

(snaps fingers) Color.

It's magical, but there's a lot of science behind it.

Let's find out what color is

and some of the amazing ways it works,

in this segment of "Physics in Motion".

♪♪

(Adrian Monte) When you look at this window, you see an array of colors.

What exactly is color anyway?

It's the part of the electromagnetic spectrum

we can see, called, logically enough,

the visible spectrum.

So, what makes us see particular colors?

Objects absorb some wavelengths of light

and not others.

The ones we don't see are the ones it absorbs,

and the colors that we do see

are those that are reflected back.

The spectrum of color ranges from violet to red,

and each color has a very specific wavelength.

Red has the longest and violet the shortest.

Just beyond our sight, at the red end,

is the infrared region of the electromagnetic spectrum,

and at the other end, the ultraviolet range.

Human sight can perceive wavelengths

from about 390 to 790 nanometers.

A nanometer is pretty short, one billionth of a meter.

How many colors are there in the universe?

It's been estimated that we distinguish between

18 decillion colors.

That's 18 followed by 33 zeroes.

A lot of choice, huh?

You may have been taught that the three primary colors

are red, blue, and yellow,

but those are the primary colors of pigments,

which are substances that add color to materials.

The primary colors of light are red, green, and blue.

But what happens when you mix all three of those?

We get this. White light.

It was that genius of physics

we've heard a lot about in this series, Isaac Newton,

who figured out that combinations of wavelengths

spread out along the visible spectrum make up white light.

So, white actually isn't a color at all.

It is the presence of all of the colors of visible light.

He also understood that what we see as black

is the absence of light.

We see color when white light is refracted

or bent at an angle.

The wavelengths are distributed along a spectrum,

what we often think of as a rainbow.

We'll talk more about color a bit later,

but there are other cool characteristics of light,

and we're in a good spot to talk about those.

See how the light comes through the window?

But the glass is not clear, is it?

If the material that light is moving through is rough,

even microscopically rough,

it will diffuse or spread out the light.

We call that kind of material translucent,

and that's what this glass is.

It's a medium that allows some but not all light

to pass through it,

so the objects cannot be seen clearly.

If no light passes through a material at all,

we say that material is opaque.

If all the light passes through a material,

like through this window, the material is transparent.

Look at this painting.

And now look at it.

Looks a lot brighter, doesn't it?

That's because the light we just turned on

is reflecting off the surface of the painting.

We call that measure of brightness luminance,

which is the amount of light reflected off a surface

measured in candelas per square meter.

The unit you might be more familiar with, lumens,

is the unit for luminous intensity,

which measures the brightness of light in a given direction.

You can see that word on any light bulb package.

It's different than wattage,

which measures the electrical power a device uses.

Luminance is inversely related

to the square of the distance from the light source.

The farther away you are, the less the luminance.

The brightness decreases at an exponential rate.

Now that we've talked about some characteristics

of the way light behaves,

we've come outside to show you something awesome

that goes on every day all over the planet.

All this green.

But why does this leaf look green?

Because it's reflecting the wavelength of green light

and absorbing all the other colors.

The chemical that makes this happen is chlorophyll,

which you might know is involved in photosynthesis.

The process that plants use to make nutrients out of light.

Chlorophyll is a light trapping pigment.

It absorbs red light,

which is the most effective wavelength

when it comes to making glucose,

a form of sugar, from light.

What we call the red edge,

near the infrared end of the spectrum,

is where photosynthesis for plants is most active.

So, we have our own little factory going on here,

powered by absorbed light

near the infrared part of the spectrum.

Let's explore more about color in our everyday world.

We brought in this color projector to do this that.

Remember, our primary colors of light

are red, green, and blue.

They are specific wavelengths of light.

When we overlap all three of them in equal intensities,

we get white light.

Where the three primary colors come together,

you can see a small triangle of white light.

Why?

What do you remember about the nature of color?

When we overlap two of the primary colors,

we get what we call the secondary colors of light,

which are yellow from combining red and green,

magenta from combining red and blue,

and cyan from combining green and blue.

That may sound familiar from your printer's ink cartridges,

and we'll talk about that more in a moment.

But what about the amazing array of colors

we can see from light?

They arise from what we call additive color mixing.

When wavelengths from different parts of the visible spectrum

overlap to create subtle, beautiful, and endless colors.

By blending different wavelengths of light

from the visible spectrum,

I can produce any color of light I want.

Within additive color mixing,

we can also produce white light using complementary colors.

These are pairs of colors which, when combined,

produce white light.

For example, some complementary combination of colors

are green and magenta, blue and yellow,

red and cyan.

When any two of them are combined,

they do a very specific thing.

Let's look at green and magenta...

now yellow and blue...

and red and cyan.

See?

All produce white light.

Each of these pairs is made of one primary color

and a secondary color.

The secondary colors themselves

are made of two other primary colors,

allowing for all of the wavelengths of light

to be present to create white light.

There's another kind of color mixing by light.

It's called subtractive.

This is when materials reflect and absorb light

rather than only reflecting it,

as in additive color mixing.

Subtractive mixing occurs when the source of color

is pigment or dye.

The refractive properties of the molecules

within the pigments and dyes

absorb some wavelengths of light and reflect others.

So, when these dyes subtract or take away the wavelengths

by absorbing them,

we are left with the colors that are reflected.

If you mix too many pigments

so that all the wavelengths are being absorbed,

what would you get?

Almost black because nothing is being reflected.

Mixing paints is the exact opposite of mixing light,

and here's an example of how painters use their properties

to create an amazing array of colors.

We can add color to objects like materials or canvas

in a few ways.

Pigment is one,

which is usually made from inorganic sources

that change the color of reflected or transmitted light

as a result of wavelength selective absorption.

Pigments are insoluble, suspended in a medium,

and don't dissolve.

For instance, cadmium sulfide is called cadmium yellow,

chromium (III) oxide is chrome green,

and iron (III) oxide is red ochre.

A dye, on the other hand, is biological in nature.

People have extracted substances from plants and insects

for thousands of years to create dyes.

Dyes are liquids or other substances

that dissolve in a medium and transmit color

when a material is soaked in it.

Our eyes perceive light with what we call rods and cones.

They are nerve cells that are photo receptors.

They absorb reflected light

and turn it into an electrical impulse,

which goes from our eyes to our brain.

We have about 120 million rods

and only about 6 or 7 million cones.

The rods are more sensitive to light than cones,

but not sensitive to color.

Cones are what perceive color,

transmitting the information about wavelengths to our brain.

These rods and cones contain molecules that absorb light

that is reflected from our surroundings.

They allow us to perceive so many awesome things.

In nature, color is used as a signal to attract,

to repel, and to disguise.

Without it, things would get pretty dull.

But, luckily, we have color all around us.

That's it for this segment of "Physics in Motion."

We'll see you next time.

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and note-taking guides,

check out the "Physics in Motion" toolkit.