Sunlight
The sun emits an enormous amount of energy, which could be harmful to human beings if not for the vapours and gases in the atmosphere, like water (clouds), ozone, and other vapours and gases in the air, through which the sunlight is filtered. In the figure it can well be seen that "cold" CO2 filters the solar radiation around 4.3 µm. The Infrared detector which uses this frequency is therefore solar blind. Not all manufacturers of flame detectors use sharp filters for the 4.3 µm radiation and thus still pick up quite an amount of sunlight. These cheap flame detectors are hardly usable for outdoor applications. Between 0.7 µm and approx. 3 µm there is relatively large absorption of sunlight. Hence, this frequency range is used for flame detection by a few flame detector manufacturers (in combination with other sensors like ultraviolet, visible light, or near infrared. The big economical advantage is, that no expensive sapphire detector windows but quartz windows can be applied. These electro-optical sensor combinations also enable the detection of none-hydrocarbons like hydrogen fires without the risk of false alarms, caused by artificial light or electrical welding.
Read more about this topic: Flame Detection
Famous quotes containing the word sunlight:
“Oh, it’s home again, and home again, America for me!
I want a ship that’s westward bound to plow the rolling sea,
To the blessed Land of Room Enough beyond the ocean bars,
Where the air is full of sunlight and the flag is full of stars.”
—Henry Van Dyke (1852–1933)
“Calm as that second summer which precedes
The first fall of the snow,
In the broad sunlight of heroic deeds,
The City bides the foe.”
—Henry Timrod (1828–1867)
“‘The key is in the window, the key is in the sunlight at the
window—I have the key—Get married Allen don’t take drugs—the key is in the bars, in the sunlight in the window.
Love,
your mother’”
—Allen Ginsberg (b. 1926)