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light
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).
The main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.
The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarisation, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation (EMR), is experimentally found to always move at this speed in a vacuum.
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics.
^ CIE (1987). International Lighting Vocabulary. Number 17.4. CIE, 4th edition. ISBN 978-3-900734-07-7.
By the International Lighting Vocabulary, the definition of light is: "Any radiation capable of causing a visual sensation directly."
^ Pal, G. K.; Pal, Pravati (2001). "chapter 52". Textbook of Practical Physiology (1st ed.). Chennai: Orient Blackswan. p. 387. ISBN 978-81-250-2021-9. Retrieved 11 October 2013. The human eye has the ability to respond to all the wavelengths of light from 400–700 nm. This is called the visible part of the spectrum.
^ Buser, Pierre A.; Imbert, Michel (1992). Vision. MIT Press. p. 50. ISBN 978-0-262-02336-8. Retrieved 11 October 2013. Light is a special class of radiant energy embracing wavelengths between 400 and 700 nm (or mμ), or 4000 to 7000 Å.
^ Gregory Hallock Smith (2006). Camera lenses: from box camera to digital. SPIE Press. p. 4. ISBN 978-0-8194-6093-6.
^ Narinder Kumar (2008). Comprehensive Physics XII. Laxmi Publications. p. 1416. ISBN 978-81-7008-592-8.
***SPF***
Great price for a sought-after Mossberg 590…
Used with unknown round count, but in good cosmetic and functioning condition.
-20” barrel, 8+1 capacity, 12ga
-Streamlight ProTac weapon light
-Heat shield, looks to be factory
-Bayonet mount
-sling mounts
-bead front sight
-4 shell...
Original owner Surefire Scout Pro M640U 1000 lumen weapon light with Z68 tailcap. Includes both MLOK and Picatinny direct mounts and original packaging. Light itself and MLOK mount are in near new condition. The replaceable flat head screw on the Picatinny mount has some subtle marring on the...
For sale, Southwest, Washington, Vancouver area, Clark county area.
Barrel band for standard stock 10/22. Replaces standard barrel band. Aluminum, with 2 portions of picatinny mount for lights or lasers. And side sling loop.
Sold the 10/22 that I used to have it on and no longer need it...
I bought a new Liberty safe and I noticed when I shut the door, I can see the LED lights shine through the sides of the door until they shut off. Has anyone else experienced this? I assumed there would be a tighter seal and wonder how that effects the heat protection.
Selling my Surefire XSC flashlight made for the Springfield Hellcat. It is 350 lumens I never mounted this and no long have the Hellcat. Selling for $200. This is made for only the Hellcat. Thanks,
I switched all my lights to the x300 & TLR-1. This grip fits my hand great, but I'm now everyday carrying a 365 comp. This holster holds a spare mag. I dremilled a small notch to fit the optic. I also heated the back to secure and slide the gas pedal, on the left side.
It is made to fit with an...
2100 lumen flashlight. USB rechargeable, or has a disposable battery adapter.
This was a well intended gift, but I have a lot of lights. $40
I can meet in Vancouver, no trades needed.
Cloud Defensive OWL light, extra battery and charger. Light has seen around 200 rounds of 5.56 and is still in excellent shape.
Price is: $250.00
Manufacturer Specs: https://www.clouddefensive.com/product/owl/
Sorry, this item has sold
Surefire classic 628 with brand new Surefire LM1-B Light Bezel (includes new Surefire battery)
The best 3-volt head upgrade for your Forend WeaponLight
500 lumens of LED white light, powered by a single 123A battery
Proprietary TIR lens delivers a far-reaching beam...
I have an extra Arken EPL-4 lightweight. 6-24x50 MOA reticle(New/in the box). MOA turrets, capped windage, 30mm body. First focal plane, illuminated reticle.
These are the new lighter weight hybrid scopes. They have EP5 internals with Japanese glass. They weigh in at 23.7 oz , while the...
Letting go of a Eclipse kydex IWB light bearing holster for the glock19 gen5 compatible with the Olight valkyrie pl-mini 2 which is included.
The kydex does have a wing on it.