299, 798 km/s. The first reasonable measurement was made by Ole Romer in 1676, then a more accurate number, 299 798 km/s, was made by Albert A. Michelson in the 1920s.

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Any device that uses light; for example, mirrors, lenses, microscopes, and telescopes

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Optical device for viewing distant objects; there are two types: reflecting and refracting telescopes

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Used a simple microscope of his own design to look at things like pond water and blood. He wrote about "little animalcules", which were actually very small organisms such as bacteria, algae, and red blood cells.

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Telescope that uses two lenses to form an enlarged image

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Telescope that uses a curved mirror and a lens to form an enlarged image

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Device for viewing distant objects; made up of two short refracting telescopes fitted together

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Diagram used to represent how light travels; each ray has an arrow to show the direction of travel

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Describes materials that allow light to pass through with little or no reflection; for example, glass

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Describes materials that allow some light to pass through

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Describes materials that do not allow light to pass through; for example, wood, metal, cardboard, etc.

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Describes objects that produce light; for example, the sun, light bulb, fire, etc.

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Describes objects that do not produce light but may reflect it (for example, the moon); most objects on earth are non-luminous

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Reflection that happens when parallel rays hit a smooth surface; all rays reflect at the same angle

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Reflection that happens when parallel rays hit a rough surface; all rays reflect at different angles

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Ray of light that arrives at a mirror or other substance

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Flat mirror; reflecting surface that has no curvature

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Line perpendicular to a surface (that is, forms a 90˚ angle with the surface)

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Angle between the incident ray and the normal

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Angle between the reflected ray and the normal

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Reflecting surface that is curved inward like the inside of a bowl or a spoon; light rays reflected from it converge (come together)

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Point at which light rays meet, or appear to meet, after being reflected by a mirror, or refracted by a lens

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Reflecting surface that bulges out like the back of a spoon; light rays reflected from it diverge (spread out)

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Bending of light as it travels from one material to another material. Ptolemy described this.

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Curved piece of glass or other transparent material that refracts light in a predictable way

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Piece of transparent material that is thinner in the middle than at the edges; light rays passing through it diverge or spread out

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Piece of transparent material that is thicker in the middle than at the edges; light rays passing through it converge or come together

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Image formed when rays meet at a point; the image can be projected onto a screen

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Model used to explain the characteristics and behaviour of light energy; it describes light as energy in the form of waves; the different colours of light have different wavelengths; waves with shorter wavelengths have higher energy than those with longer wavelengths

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Colours of visible light; the colours in a rainbow or viewed when light is split by a prism

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All forms of radiant energy: visible light, infrared radiation, ultraviolet radiation, radio waves, X-rays etc.

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Refers to the whole range of wavelengths of visible and invisible electromagnetic radiation

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Electromagnetic radiation used in communications around the world

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Electromagnetic radiation that has a shorter wavelength than radio waves and carries more energy; used to cook food and transmit audio and video signals

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Acronym for radio detection and ranging; system that detects reflected microwaves

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Electromagnetic waves that have more energy than visible light; too much ultraviolet radiation can increase the risk of skin cancer

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High-energy electromagnetic radiation with the shortest wavelength; used to treat some types of cancer

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Form of artificial light; uses electrical energy to heat a thin wire thread that glows white hot

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Form of artificial light; uses ultraviolet light waves to make the coating inside an opaque tube glow white

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Substance that emits light when exposed to ultraviolet radiation

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Process in which a substance emits light after it has absorbed ultraviolet light

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The ability of certain organisms to produce light by a chemical reaction

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Light-producing organ found in bioluminescent organisms

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Red, green, and blue light; adding these three colours of light produces white light

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Yellow, cyan, and magenta; colours made from adding any two primary colours of light

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Theory that explains what happens when coloured lights are mixed together

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Opening in the eye that lets in light

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Hole or opening in a camera that lets in light

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Band of muscle in the eye that controls the size of the pupil and the amount of light entering the eye

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Part that changes the size of a camera’s aperture; it varies the amount of light that reaches the film

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Part that acts like a door to control the amount of light entering a camera

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Special lining on the back of the eye; when light hits the retina, receptor cells send messages to the brain, which translates them into an image

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Light-sensitive cells found in the retina of the eye; there are two types: rods and cones

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Nerve that leads from the retina to the brain

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The layer of the eye lying between the retina and the sclera. Rich in blood vessels, provides oxygen and nourishment to the parts of the eye.

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The transparent front part of the eye that covers the iris, and pupil. Protects the eye from dust and germs, providing most of an eye's optical power.

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The clear aqueous solution  that fills the space between the lens  and the retina. Solution of 99% water,  but has a gelatinous viscosity two to  four times that of water.

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Liquid that fills the area between the cornea and the lens. Is produced by the ciliary body, nourishes the cornea and the lens, gives the eye its shape

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Specialized cells in the retina that detect colour; there are three types of cones, each sensitive to different colours: red, green, and blue.

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Specialized cells in the retina that are sensitive to low levels of light

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Eyes that are round and have a cornea, a lens, and a retina

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Describes animals that are active at night

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Animals have another part to the eye. A reflective surface between the retina and the sclera. Reflects light back to the retina allowing the animal to see well at night.

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Eyes that are made up of many smaller units; found in insects and crustaceans

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Unit of a compound eye; has a lens, focusing cone, and light-sensitive cell (plural ommatidia)

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Process of creating an image using a computer

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Short for picture element; individual element of a digital image

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The number of pixels per unit area in a digital image

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Provides clear central vision

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Located in the centre of the macula and provides the sharpest detailed vision.

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Tough white outer coating that covers your entire eye, except the cornea

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