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Properties of Light

Characteristics of the electromagnetic spectrum.

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Those Yellow Sodium Lights

Those Yellow Sodium Lights

Credit: Dave Worley
Source: http://www.flickr.com/photos/greeblie/2027362850/
License: CC BY-NC 3.0

When you drive through a long tunnel, there are lights along the way to illuminate the road. Increasing, these lights utilize either low-pressure or high-pressure sodium technology to provide more energy efficiency and lower cost.

Why It Matters

  • A sodium light consists of an evacuated tube containing electrodes and metallic sodium. Often, the light also contains mercury to help heat the system. As current flows through the electrode, the metal is heated. In the vapor state, the sodium electrons are excited to higher energy levels  When these electrons return to a lower energy level, light is given off. The yellow color is a product of the light emitted by the sodium electrons. Since it is not a color that many people care for, other metals are often included to alter the wavelength of the emitted light.
  • Credit: Matt Doughty
    Source: http://www.flickr.com/photos/mjdoughty/5388803628/
    License: CC BY-NC 3.0

    Sodium lights being used on a busy street in Beijing [Figure2]

  • Although the sodium light requires less energy that other types of light and is more efficient, there are drawbacks to the use of these light sources. Metallic sodium reacts with the moisture in the air and can explode if the bulb is broken. If mercury is incorporated into the system (which is often the case), this metal is also very toxic. Disposal therefore becomes more complicated since these bulbs cannot be disposed of in a garbage can.
  • Watch the videos contained in the first link listed below to see the construction and operation of sodium lights.

Explore More

With the links below, learn more about sodium lights. The answer the following questions.

  1. What was a major problem in producing a high-pressure sodium lamp? How was this problem solved?
  2. Were metal halide lamps more or less effective than high pressure sodium lamps in giving a sense of safety?
  3. Why do LED lights appear to provide better illumination than sodium lights?
  4. What type of growth is produced in plants by metal halide lights? by sodium lights?

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Image Attributions

  1. [1]^ Credit: Dave Worley; Source: http://www.flickr.com/photos/greeblie/2027362850/; License: CC BY-NC 3.0
  2. [2]^ Credit: Matt Doughty; Source: http://www.flickr.com/photos/mjdoughty/5388803628/; License: CC BY-NC 3.0

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