How Light Travels

Light can pass through some materials and not others. ​Transparent materials let nearly all light pass through them. Examples are gas and air. Translucent materials allow some light to pass through. Opaque materials do not allow any light to pass through. Wood and metal are opaque.

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Light can travel in a vacuum. Light in a vacuum travels in a straight line.

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Stained glass such as these are translucent. ​Light comes through but not completely.

​Brightness

​Brightness is the amount of light that the eye receives from a source. The brightness of light depends on two things. First, a light looks bright if it is intense. Intensity is the actual amount of light that a source gives off. Second, a light looks brighter if it is close.