Chapter 16Fundamentals of Light

• The Ray Model of Light

-light is represented by a ray that travels in a straight path

-can only be changed by placing an obstruction in its pathsheyrocks

Sources of Light

1. Luminous Source- an object that emits light2. Illuminated Source- an object that reflects light;

depends on the mediaa. Opaque media-prevents light from passing throughb. Translucent- allows light through but object appears fuzzyc. Transparent-allows light and object can be seen clearly

Quantity of Light

• Luminous Flux-amount of light produced per unit of time- has the symbol P- Measured in Lumens(lm)

•Illuminance- the rate at which light strikes an object- Has the symbol E- Measured in Lux(lx)= lm/m2

- E=P/4r2

Illumination of a Surface

• What is the illuminance at on you desktop if it is lighted by a 1750-lm lamp that is 2.50 m above your desk.

• E=P/4r2

• E= 1750 lm/4(2.50 m)2

• E= 22.3 lx

The speed of light

• Light is an electromagnetic wave• It carries energy • The only portion of waves that can be seen

by the human eye

• Electromagnetic spectrum consists of:• Radio, microwave, infrared, visible,

ultraviolet, X-rays, Gamma rays

Light cont.

• As you go from left to right from the list:• Radiolong , low frequency, more wavelike• Gamma rays short , high frequency, more

particle like

• Visible Light consists of what colors:• Red, orange,yellow, green, blue, indigo, and violet

• Speed of light(c) = 3.00 x 108 m/s

The Wave Nature of Light

1. Diffraction- bending of light around a barrier

2. Color

Why do objects appear to have certain colors?

a. They reflect that particular color(wavelength)

b. Atoms/molecules in an object have certain natural frequencies at which they selectively absorb energy

Color cont.

1. Additive Primary Colors

Red, Blue, Green

-when added together, will produce white light

- primary colors when mixed produce the secondary colors :

yellow= red + green

magenta= red + blue

cyan= blue + green

Color cont.

2. Subtractive Primary Pigment colors

Cyan, magenta, yellow

-absorbs only one primary color and reflects two from white light

Cyan absorbs red, reflects blue and green

magenta absorbs green, reflects red and blue

Yellow absorbs blue, reflects red and green

Polarization of Light

• - production of light in a single plane of oscillation

• Light produced from a bulb or the sun is unpolarized lightit vibrates in more than one plane, i.e., horizontal and vertical planes

How does polarization occur?

1. By Filtering with a Polaroid Filter

- the Polaroid filter is made of a special material which is capable of blocking one of the 2 planes of vibration

-after it has been filtered, it will only have ½ the light intensity

Polarization cont.

2. By Reflection

-light can be polarized off of a nonmetallic surface ( road surface or water) because the reflected light has a large concentration of vibrations in a parallel plane to the surface

Metallic surfaces reflect a variety of vibrational directionsunpolarized light