absorption: the taking in of light; not reflected

angle of incidence: the angle between the incident ray and the normal

angle of reflection: the angle between the normal and the reflected ray

bend: a change in the direction of light as it passes from one medium to another; refraction

centerline: the imaginary line that passes through the center of the lens surface and that is perpendicular to the surface of the lens at that spot; also called the optical axis of the lens

concave: a surface that curves in on itself, like the inside of a bowl concave lens: a lens that is thicker at the edges than at the center

converge: to move together toward a central point. When light rays from an object converge, they form an image of the object.

convex: a surface that curves outward, like the outside of a bowl

convex lens: a lens that is thicker at the center than at the edges

curvature: a measure of the amount of curving. The curvature of a lens is what causes light rays to bend.

diffuse reflection: the random reflection of light from a rough surface, which results in a fuzzy, scattered reflection

dispersion of light: the separation of light into colors

electromagnetic spectrum: the full set of waves that can travel through space; includes not only visible light but shorter waves, such as X -rays, and longer waves, such as radio waves

electromagnetic wave: a wave that is both electric and magnetic in nature and that can travel through a vacuum, e.g., light waves, radio waves, microwaves

emission: the giving off of light energy: the ability to do work or cause change (so hot that heat energy turns into light energy, e.g., light bulb)

filter: an object that blocks some colors and lets others through

focal length: the distance between the center of a lens or mirror and the focal point

focus or focal point: the point on the centerline of a lens or mirror at which reflected or refracted rays converge

food chain: an illustration of feeding relationships in an ecosystem using a single representative from each of the trophic levels

frequency: the rate at which something happens during a specific period of time

herbivore: an organism that eats plants

incident ray: a ray of light that falls directly on a surface

index of refraction: the ratio of the speed of light in a vacuum to the speed of light in a substance

laser: light rays of uniform size, color, and phase, focused on a single point

lens: any transparent material that refracts light; curved, transparent objects that change the path of light rays

light: that part of the electromagnetic spectrum that stimulates the retina and enables sight; an electromagnetic phenomenon

mirrors: opaque objects that reflect light rays

normal: a line that is perpendicular to the mirror at the spot the ray hits. The angle at which light hits a surface is measured from the normal.

opaque: objects that do not transmit light, e.g., a brick, a mirror. Opaque objects absorb or reflect the light.

partial reflection: the light that is reflected back as it passes from one medium to another

photon: a pulse of electromagnetic radiation emitted when electrons drop from a higher to a lower energy level. Photons are light particles.

photosynthesis: the process by which plants convert light energy from the Sun, water, and carbon dioxide to chemical energy to produce oxygen and sugars

plane mirror: a mirror with a perfectly flat surface

prism: a special lens that splits white light into a spectrum of color

producer: an organism in a food chain that makes its own food. Producers are the first level in the food chain.

radius of curvature: the amount of curvature of a shape. The term is often followed by a quantity that describes the radius of a circle whose circumference would match the shape being described.

ray: a straight line that represents the path of a narrow beam of light, usually from the source

reflected ray: a ray of light that has bounced off a surface reflection: the bouncing of light off an object; bounced back

refraction: the bending or change in the direction of a light wave as it passes from one medium into another of different density

retina: the light-sensitive lining of the back of the eye that receives images formed by the lens, converts them into electrical signals, and transmits them into the optic nerve

scattered light: light reflected in various directions

sight: the act of seeing

spectrum: a range of color arranged according to wavelength

speed of light: the velocity of light in a vacuum; 299,792,458 meters per second

translucent: objects that let some light through, but with some distortion of its path. Images are not seen well through translucent objects, e.g., wax paper, sheer fabric.

transmission: the passing of light through a space or medium

transparent: objects that transmit all light without distorting its path. Images can be seen through transparent objects, e.g., clear glass.

trophic level: the division of species in an ecosystem on the basis of their main nutritional source (e.g., producers, first-order consumers, second-order consumers, predators)

visible light or visible spectrum: the section of the electromagnetic spectrum that can be seen by the human eye; between the range of 360 to 740 nm

wave: a disturbance that transfers energy through matter or space

wavelength: the distance between two adjacent crests or troughs of a wave

white light: a mixture of all colors of light. Sunlight is white light.