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Thread: Why do police radar guns use microwaves?

  1. #1 Why do police radar guns use microwaves? 
    Time Lord
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    Why not visible light? Is the amount of Doppler Shift due to a car's speed harder to determine for visible light?


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  3. #2  
    Administrator KALSTER's Avatar
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    I will guess at two reasons:

    1) It might not be a good idea to effectively shine a torch into oncoming traffic.
    2) Visible light is more prone to bending and absorption than microwaves, both by the air and by the car.


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  4. #3  
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    Actually, it is used. It's called LIDAR. Due to its shorter wavelength it can be used to pick out a single car from a stream of traffic. However, it would also be more sensitive to fog or dust.
    http://en.wikipedia.org/wiki/Lidar#M...aw_enforcement
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  5. #4 Re: Why do police radar guns use microwaves? 
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    Quote Originally Posted by kojax
    Why not visible light? Is the amount of Doppler Shift due to a car's speed harder to determine for visible light?
    Laws are passed against use of police radar detectors. They want to catch you unawares. If the illuminator were recognizable, maybe too many drivers stomping on the brake pedal might lead to pileups.

    Visible light offers the prey the simple stealth strategy implicit with black paint jobs.
    "Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense." --Buddha (563BC-483BC)
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  6. #5  
    Administrator KALSTER's Avatar
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    We should all grow carbon nanotube forests as a paint job. Let's see them catching us then. 8)
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  7. #6 Re: Why do police radar guns use microwaves? 
    Forum Freshman
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    Quote Originally Posted by kojax
    Why not visible light? Is the amount of Doppler Shift due to a car's speed harder to determine for visible light?
    Too much interference in the day from that big lamp in the sky and at night from headlamps.
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