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• Light travels as a transverse wave and moves in straight lines.
• Light can pass through transparent and translucent materials, but not opaque materials.
• Ray diagrams use straight lines to represent rays of light, arrows show the direction the light travels in.

Light travels as waves. These are transverse waves, like ripples in water. The direction of vibration in the waves is at 90° to the direction that the light travels.

Unlike sound waves, light waves can travel through a vacuum – they do not need a substance to travel through.

Light can pass straight through transparent materials.

Transparent substances, like water and glass, allow light to pass through them. This means objects can be seen clearly through a transparent substance.

Translucent materials allow some light to pass through them.

In translucent materials, not all light passes through and sometimes it changes direction, therefore images viewed through translucent materials are visible but do not appear clearly and are often distorted. For example frosted glass on a shower door.

Examples of translucent objects include ice, thin fabrics and greaseproof paper.

Opaque materials are substances which light cannot pass through, like stone, metal or wood.

The light is absorbed, scattered or reflected – so it does not pass through the material.

Luminous objects, like the Sun, can be seen because they produce their own light. The light travels in a straight line directly from the source to your eye.

Non-luminous objects, like the Moon, do not produce their own light, but they can be seen because they reflect light from luminous objects. The light travels in a straight line directly from the object to your eye.

Ray diagrams are used to show the path that light takes. The rays of light are represented using straight lines, with an arrowhead to show the direction the light is travelling.