Light

What you see depends on the amount of light in the room and the color of the objects. For you to see an object, it must reflect some light back to your eyes.

Objects can 1. absorb light 2. reflect light 3. transmit light

The type of matter determines the amount of light it absorbs, reflects and transmits. Opaque materials only absorbs and reflects light. No light passes through it.

Translucent materials allow some light to pass through them, but you cannot see clearly through them. Transparent materials transmit almost all the light striking them so you can see clearly through them. Very little light is absorbed or reflected.

Reflection of light occurs when a light wave strikes an object and bounces off. This is happening when you look in a mirror. Because light behaves as a wave it obeys the law of reflection.

According to the law of reflection, the angle at which a light wave strikes a surface is the same as the angle at which light is reflected.

Why can you see your reflection in a store window but not in a brick wall? Answer: smoothness of the surface. The smooth glass reflects back in only one direction while the rough brick reflects in many directions.

Refraction is caused when the wave changes speed moving from one material to another. Like air to water. Every material has an index of refraction. This property of the material that indicates how much the speed of light in the material is reduced.

Examples of refraction of light: Prisms Rainbows Mirage

Colors An object’s color depends on the wavelength of light it reflects. White light is a blend of all colors of visible light. Black is not a color that is present in visible light. Objects that appear black absorb all colors and reflect nothing back.

How do you see color? Your eyes have different cones that respond to different ranges of wavelengths. Red cones respond to red and yellow waves Green cones respond to green and yellow waves. Blue cones respond to blue and violet waves.

Your brain interprets color based on the reflected light of the object and how the cones in your eyes respond.

The three primary colors of light are red, green and blue. They correspond to the three different cones in your retina and when mixed together in equal parts they produce white light.

Most light bulbs in your house produce incandescent light. The light is generated by heating a piece of wire coil until it glows. 90% of energy given off by the incandescent bulbs is thermal energy.

Florescent light uses phosphors to convert ultraviolet light to visible light. Florescent bulbs used 1/5 of the energy that incandescent bulbs use which relates to lower energy costs.

Neon lights are glass tubes filled with gas. When the electric current flows through them and the electrons collide with the gas molecules visible light is produces. If the tube only contains neon gas then the light produced is bright red. Other gases must be added to produce additional colors.

Sodium vapor lights are used for street lights and other outdoor lights. The bulb contains a mixture of neon gas, argon gas and sodium metal. When heated it produces a yellow- orange glow.

Tungsten-Halogen lights produce an intense bright light. These bulbs mix a gas with a tungsten filament. When heated the filament becomes much hotter than the incandescent filament, hence the brighter light. Used on movie sets and on underwater cameras.

Lasers are used for a variety of purposes in the world. Laser light begins when a large number of light waves are emitted at the same time. Most common laser material is a helium-neon laser.

Total internal reflection occurs when light traveling from one medium to another is completely reflected at the boundary between the two materials.