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For details about the Planetary Boundary Layer, see this article by Jeff Haby, and part 2 of an article about lasers in the atmosphere from Larry McNish of the Royal Astronomical Society of Canada.

For a more powerful 50 mW green laser, the green “dot” is visible well over 7 miles -- even though to the user, the beam appears only a few hundred meters long. What is happening?The Planetary Boundary LayerFor a laser beam to be visible, some of the light must reflect off particles such as dust, smoke or water vapor. In a zone near the earth’s surface, the atmosphere is full of these aerosols, helping to make outdoor laser beams visible.But above the Planetary Boundary Layer (also known as the Atmospheric Boundary Layer), air is much cleaner. After the beam exits the PBL and enters cleaner air (fewer aerosols), much less light is reflected back. The beam seems to disappear.The PBL thickness can vary from day-to-day and at different locations. Typically, it is a few hundred meters, up to a maximum of a few thousand meters. The illustration below shows the PBL:

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Correlated Color Temperature (CCT) can be defined as the color of white light a light source is emitting. CCT is measured in Kelvin (K). The different color temperatures along the Kelvin scale correlate with different shades of white light, all of which impact how an individual perceives the space. LED lights are typically grouped into 3 different color temperatures: warm white, natural white, and cool white. Warm white gives off a yellow shade of light, natural light closely resembles the color of light given off from the sun, and cool light has a slightly blue tint to it.

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However, this is a dangerous illusion. A person can think their laser beam can’t reach an aircraft, since the beam looks “short”. They are of course mistaken.Light from a laser does not stop in mid-air, but continues going. A pilot at the other end can clearly see the light from even a relatively low powered 5 mW green laser, at a distance well over 2 miles.

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Correlated Color Temperature (CCT) can be defined as the color of white light a light source is emitting. CCT is measured in Kelvin (K). The different color temperatures along the Kelvin scale correlate with different shades of white light, all of which impact how an individual perceives the space. LED lights are typically grouped into 3 different color temperatures: warm white, natural white, and cool white. Warm white gives off a yellow shade of light, natural light closely resembles the color of light given off from the sun, and cool light has a slightly blue tint to it.

Based on a NOAA diagram. We Photoshopped this into a nighttime view, to illustrate how a laser beam appears much brighter to the person holding it, as the beam passes through the aerosol-filled Planetary Boundary Layer only a few hundred meters above the earth’s surface.