Light and ColorLight and Color

Standard: S8P4c. Explain how the human eye sees objects and colors in terms of wavelengths.

EQ: How do humans like yourself see color?

Part 1 – Properties of Part 1 – Properties of LightLight

Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

Light travels much faster than sound. For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

The Electromagnetic SpectrumThe Electromagnetic SpectrumThe electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

Visible LightVisible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. Each color has a different wavelength that our eyes register.

Color

ROY G BIV is the order…. •From longest wavelength to shortest •From lowest frequency to highest •From lowest energy to highest•These 7 colors combined make up white light which is light from the sun (radiant energy).

ColorColor

White light is not a single color; it is made up of a mixture of the seven colors of the visible light spectrum.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

How do we see objects?We see objects because the objects reflect light into our

eyes:

Homework

How do we see Color?How do we see Color?

1. All the colors of the visible light spectrum shine on the apple.2. The surface of a red apple absorbs all of the other colors of the spectrum, except for red, and reflects red to the human eye.3. Humans would not be able to see color or objects without LIGHT!! Light has to reflect off an object in order to see it.

Seeing colorSeeing colorThe color an object appears depends on the colors of light it reflects.

For example, a yellow book only reflects yellow light:

White

light

Only yellow light is

reflected

When a person sees white, all the colors of the spectrum are being reflected off the object back to the eye. A white hat would reflect all seven colors.

A pair of blue pants would reflect only blue light to the eyes.

Blue Light reflected to

eyes

All colors reflected

to the eyes

White

light

White

light

Using coloured lightUsing coloured light

When a person sees black, all the colors of the spectrum are being absorbed by the object. There’s no reflection of color back to the eye so the object looks black.

White

light

Shirt looks black. No light is reflected to the eyes.

Now you tryNow you try

• Determine how you see the colors of the following objects: