Light and ColorLight one candle and chase away the

night

Electromagnetic Waves

Non Mechanical Waves – this means they do not need a medium to carry them. Transverse Wave They travel through a vacuum They work through the electrical

and magnetic fields

Electromagnetic Spectrum

Classification of electromagnetic waves according to frequency

No sharp boundary between regions

All travel at the same relative speed called the speed of light - c

Transparent Materials

How light penetrates transparent material such as glass:

Transparent Materials

Average speed of light through different materials• vacuum—c (300,000,000 m/s)• atmosphere—slightly less than c (but rounded off

to c)• water—3/4 c• glass— 2/3 c, depending on material• diamond—4/10 c

All EMW travel at the same speed.

Transparent

So we see that glass is transparent to visible light, but not to ultraviolet and infrared light.

Opaque Materials

Most things around us are opaque—they absorb light without re-emitting it. Books, desks, chairs, and people are opaque.

Vibrations given by light to their atoms and molecules are turned into random kinetic energy—into internal energy. These materials become slightly warmer.

Opaque Materials

Shadows A thin beam of light is often called a

ray. When we stand in the sunlight, some

of the light is stopped while other rays continue in a straight-line path.

We cast a shadow—a region where light rays do not reach.

Seeing Light – The Eye

The retina is composed of tiny antennae that resonate to the incoming light.

• Rods handle vision in low light.– They predominate toward the

periphery of the retina.• Cones handle color vision

and detail.– They are denser toward the

fovea.– There are three types of cones,

stimulated by low, intermediate and high frequencies of light.

Seeing Light – The Eye

Although our vision is poor from the corner of our eye, we are sensitive to anything moving there.

Seeing Light – The Eye

The brightest light that the human eye can perceive without damage is some 500 million times brighter than the dimmest light that can be perceived.

Lateral inhibition: We don’t perceive the actual differences in brightness. The brightest places in our visual field are prevented from outshining the rest.

Seeing Light – The Eye

The brightest light that the human eye can perceive without damage is some 500 million times brighter than the dimmest light that can be perceived.

Lateral inhibition: We don’t perceive the actual differences in brightness. The brightest places in our visual field are prevented from outshining the rest.

Seeing Light – The Eye

Seeing Light – The Eye

Seeing Light – The Eye

Seeing Light – The Eye

Seeing Light – The Eye

Seeing Light – The Eye

Color in Our World

Color we see depends on frequency of light.

Lowest frequency—perceived as red In between lowest and highest

frequency—perceived as colors of the rainbow (red, orange, yellow, green, blue, indigo, violet)

Highest frequency—perceived as violet

Beyond violet, invisible ultraviolet (UV)

Stroop Effect

Read the following using the color of the word – not the word itself.

Color in Our World

Color Physiological experience In the eye of the beholder

Selective Reflection

Objects reflect light of some frequencies and absorb the rest.• Rose petals absorb most of the light and

reflect red.• Objects that absorb light and reflect none

appear black.• Objects can reflect only those frequencies

present in the illuminating light.

Selective Transmission

Color of transparent object depends on color of light it transmits.

Colored glass is warmed due to the energy of

absorbed light illuminating the glass.

Mixing Colored Light

Additive primary colors: Red, green, and blue Produce any color in the spectrum

Mixing Colored Light

Subtractive primary colors Combination of two of the three additive primary colors:

red + blue = magenta (subtracting green) red + green = yellow (subtracting blue) blue + green = cyan (subtracting red)

Mixing Colored Light

Only three colors of ink (plus black) are used to print color photographs—(a) magenta, (b) yellow, (c) cyan, which when combined produce the colors shown in (d). The addition of black (e) produces the finished result (f).

Why is the sky Blue???

Sun emits white light.Light passes through the atmosphere.Blue light is scattered. Smaller wavelengths scatter the most. No atmosphere means no blue light scatteringSun appears yellow because blue is removed – green/red

Why Sunsets Are Red

Light that is least scattered is light of low frequencies, which best travel through air.• Red • Orange • Yellow

Colors

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Colors

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