Night Time Humidity

Fun facts, useful in social gatherings . . .

When sunlight streams through the air, it moves through the air with almost perfect efficiency. When it eventually strikes a surface it either is reflected away, still in the form of light energy, or it is converted into heat energy. One or the other or some combination of both must happen, because a basic law of physics is that energy is conserved.

The ability of light to move through the air with near-perfect efficiency is the result of the wavelength of light energy. When the light strikes an object such as the ground, and it is converted into heat, it will attempt to radiate away through the air, but at a different wavelength associated with heat rather than light.

The wavelength of heat energy passes through dry air easily, but it does not transfer well through moisture. So, if the air is humid, the heat is trapped close to the earth, thereby keeping the air warm. When humidity is high, this heat will keep things hot and sticky all night long.

If the air is dry, the heat will radiate through the air, back out into space. This is why desert areas can see daytime temperatures well above 100 degrees Farenheit, but night-time temperatures may drop below freezing.

It’s all about two things: the wavelengths of light versus heat, and the amount of moisture in the air.

Here’s another related fact: when light encounters your car’s windows, it passes through easily. When it strikes the interior and is converted into heat energy, the wavelength change no longer allows it to exit through the glass. So this is part of the reason why a car gets so very hot in sunlight, and why a reflector behind the windshield can make a difference: it sends the light energy back out, before it can get converted to heat energy.