Page 39 - Curriculum Visions Dynamic Book

 A tunnel is lit by sodium discharge tubes. The picture on the left shows the detail.
fluorescent: a substance that gives out visible light when struck by invisible waves such as ultraviolet rays.
vapour: the gaseous form of a substance. For example, water vapour is the gaseous form of liquid water.
 Sodium lights are only one of a range
of elements used to create lighting. Many “neon” lights are elemental colours; for example, neon gives out a red light in a discharge tube. Most metal filaments in incandescent bulbs produce a yellow–white light. A panorama of a city at night will show many of these colours, but almost certainly sodium lights will dominate as they are efficient and relatively cheap.
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