Light 3-3 Illuminated- object that can be seen because it reflects light Luminous- object that gives off its own light Common types of lights: IncandescentFluorescentNeon Sodium vapor Tungsten-halogen

Light 3-3  Incandescent lights- glows when a tungsten filament gets “white hot” not efficient 10% visible light and 90% infrared (why a bulb gets hot) not efficient 10% visible light and 90% infrared (why a bulb gets hot)  Fluorescent lights – glass tube that contains gas and powder. When electrical current goes through the tube the gases give off ultraviolet waves that hit the powder which produces visible lights

Light 3-3  Neon lights – different gases are placed in a sealed tube, electricity is sent through the tube, the gases absorb the energy for a short time. Give off the energy as different colored light.  Sodium Vapor lights – solid sodium, neon and argon gas a placed in the light, the gases are heated by electricity, sodium changes from solid to gas, sodium begins to give off yellow light

Light 3-3  Tungsten-halogen lights- contain tungsten filament and a halogen gas, electricity makes the filament glow, halogen gas makes the filament give off bright white light.  Bioluminescence – chemical reaction between proteins and oxygen in an organism. Almost all light not heat

Light 3-4  Parts of the eye:  Cornea- transparent lens on the front of the eye bends light rays, protects against dust, cleaned and moistened by the eyelid  Iris- “colored” part of eye, ring of muscle that contracts or expands to change the amount of light that enters the eye  Pupil- looks black is actually a hole covered by cornea. In dim light the iris expands exposing more of pupil (letting more light in) In bright light the iris contracts making the pupil smaller (letting less light in)

Light 3-4  Lens – convex lens that refracts an image on the lining of your eyeball. Muscles contract or expand to change the lens depend on how close or far away the object is.  Retina- made of millions of cells called rods and cones, an upside down image of what you see is refracted on to the retina. Rod- detect white, black, and gray help you see dim light and night vision Cone – respond to color cones for red, green, and blue only work in bright light

Light 3-4  Optic nerve – thick nerve that sends the signal to the brain brain combines the two images into one 3-D image and flips the image right side up. Nearsighted -can see objects that are near, difficulty with far way objects. eyeball is too long, corrected with concave lenses Farsighted- can see objects that are far, difficulty with near objects, corrected with a convex lenses