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:
“Love is the hardest thing in the world to write about. So simple. You’ve got to catch it through details, like the early morning sunlight hitting the gray tin of the rain spout in front of her house. The ringing of a telephone that sounds like Beethoven’s “Pastoral.” A letter scribbled on her office stationery that you carry around in your pocket because it smells of all the lilacs in Ohio.”
—Billy Wilder (b. 1906)
“Anton Petrovich turned into the passage, followed the arrow to men, mankind, human beings, marched past the toilet, past the kitchen, gave a start when a cat darted under his feet, quickened his step, reached the end of the passage, pushed open a door, and a shower of sunlight splashed his face.”
—Vladimir Nabokov (1899–1977)
“Semi-Saracenic architecture, sustaining itself as if by miracle in mid air; glittering in the red sunlight with a hundred oriels, minarets, and pinnacles; and seeming the phantom handiwork, conjointly, of the Sylphs,... the Fairies,... the Genii, and ... the Gnomes.”
—Edgar Allan Poe (1809–1849)