Sodium street lamps and the light they emit

In summary, the speaker observed that objects appeared different under sodium street lamps compared to what they expected based on their understanding of light. They explained that when white light is shone on a red object, the object appears red because it absorbs all non-red light and reflects the red light. However, under sodium light, the speaker could still make out some colors, such as green and brown, but had difficulty determining the color of cars except for silver ones. The speaker mentioned that this was surprising, as they expected only objects with a similar wavelength to sodium light to appear as silhouettes. They welcomed any comments or suggestions on this topic.
  • #1
AStaunton
105
1
when looking at objects illuminated by sodium street lamps, I felt that they appeared somewhat different from what expected from my (somewhat naive) understanding of light. My knowledge is (and I'm talking only about visible light) that if something is red, and white light is shone upon it, this object absorbs all light from the white light that isn't red and reflects the red light and so the object appears red and similarly for any other colour. so for example taking the red object again, if we now shine blue light upon it, the red object absorbs this light and as this time there is not red light to reflect it simply appears black or as a silhouette.

so going back to the sodium street lamp, when I looked object illumanited by it, I could still kind of make out their colour, for example the green of hedges I think I could make out and the browney colour of the bark of trees...looking at cars, mostly their colour was very hard to determine and they did appear quite dark maybe even silhouette like with the exception of silver cars, they still looked very silver.

As the visible lines of sodium is predominantly a doublet of yellow lines (I think of around 500nm but maybe I'm wrong) I would expect anything that is not a colour of this wavelength to appear as a silhoutte, but as I said above this was not the case.

Appreciate any comments or suggestions about this. Thanks
 
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  • #2
High pressure sodium lamps emit a bit of a wide enough spectrum to distinguish some colors. Low pressure sodium light makes yellow look orange and every other color look black for the reason you described.
 

1. What is the purpose of sodium street lamps?

Sodium street lamps are used to provide lighting on public streets and highways. They help improve visibility for drivers and pedestrians, as well as increase safety at night.

2. How do sodium street lamps produce light?

Sodium street lamps emit light through a process called "sodium vaporization." This involves heating up a small amount of sodium metal inside the lamp, causing it to vaporize and produce a bright yellow-orange light.

3. Why is the light from sodium street lamps yellow in color?

The light emitted by sodium street lamps is yellow because of the high concentration of sodium vapor inside the lamp. The vapor is excited by the electrical current passing through it, causing it to emit a specific wavelength of yellow light.

4. Are there any disadvantages to using sodium street lamps?

One disadvantage of sodium street lamps is that they can create a glare for drivers and pedestrians, which can be distracting and potentially dangerous. They also have a narrow spectrum of light, making it difficult to accurately perceive colors under their illumination.

5. How do sodium street lamps compare to other types of street lighting?

Sodium street lamps have a longer lifespan and are more energy efficient compared to other types of street lighting, such as incandescent or fluorescent bulbs. However, they do not produce as much light as other options and can be more expensive to install and maintain.

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