Ultimately, absorption of electromagnetic radiation requires the generation of the opposite field, in other words, the field which has the opposite coefficient in the same mode. A good demonstration of this is color. If a material or matter absorbs light of certain wavelengths (or colors) of the spectrum, an observer will not see these colors in the reflected light. On the other hand if certain wavelengths of colors are reflected from the material, an observer will see them and see the material in those colors. For example, the leaves of green plants contain a pigment called chlorophyll, which absorbs the blue and red colors of the spectrum and reflects the green. Leaves therefore appear green, whereas reflected light often appears to the naked eye to be refracted into several colors of the spectrum (i.e. a rainbow effect).

For one, it frees you to move around your scene or set and measure light in different areas. It allows you to conduct what’s called “incident metering” – meaning when you measure the amount of light falling onto your subject, rather than the amount of light bouncing off it, which is what your camera’s system is measuring when you point it at something.

Sources: http://en.wikipedia.org/wiki/Absorption_%28electromagnetic_radiation%29 http://hyperphysics.phy-astr.gsu.edu/hbase/biology/ligabs.html http://www.physicsclassroom.com/class/light/u12l2c.cfm http://www.andor.com/learning/light/?docid=333 http://www.chemicool.com/definition/absorption_of_light.html http://hyperphysics.phy-astr.gsu.edu/hbase/biology/photosyn.html#c1

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A light meter is as it sounds – a device for measuring the available light in a scene so that you can set your camera’s exposure accordingly. Yes, all modern cameras have their own built-in metering systems. However, a light meter offers a number of advantages that makes it a useful tool for those who require precise exposure accuracy.

This is called ‘reflected metering’. While it’s a good, reliable way to get a quick reading of a scene, it is easily compromised by variances in tone and colour in different subjects. Subjects that are lighter than neutral grey – white snow, wedding dresses, etc – will appear brighter than they are, causing the camera to underexpose. Meanwhile, subjects darker than neutral grey, like a black cloth or a black cat, will reflect less light and cause the camera to overexpose.

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[/caption] Those who can remember sitting through elementary science class might recall learning that with all matter, light is absorbed and converted into energy. In the case of plants, this process is known as photosynthesis. However, they are by no means the only species or objects that do this. In truth, all objects, living or inorganic are capable of absorbing light. In all cases, absorption depends on the electromagnetic frequency of the light being transmitted (i.e. the color) and the nature of the atoms of the object. If they are complementary, light will be absorbed; if they are not, then the light will be reflected or transmitted. In most cases, these processes occur simultaneously and to varying degrees, since light is usually transmitted at various frequencies. Therefore most objects will selectively absorb light while also transmitting and/or reflecting some of it. Wherever absorption occurs, heat energy is generated.

We have written many articles about the absorption of light for Universe Today. Here’s an article about absorption spectra, and here’s an article about absorption spectroscopy.

Light meters can be an invaluable tool for photographers and videographers alike. Whether you shoot in the studio or on location, having a reliable light meter at your disposal is a time-honoured way of making sure you get accurate exposures, time and again.

We’ve also recorded an entire episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.

One particular use for a hotshoe-mounted camera light meter is if you shoot film. Many analogue photographers use second-hand vintage SLRs or large-format cameras, and often on these old cameras, the first thing to fail is the built-in light meter (if it even has one in the first place).

If you’d like more info on light absorption, check out an article about Light Absorption, Reflection, and Transmission. Also, here’s an article about reflection and absorption of light.

In genres like professional portrait or product photography, it is critically important to get accurate, balanced exposures. With a light meter you can ensure that your studio lights are at just the right level relative to each other, that your flash is firing at the correct intensity, and more. A light meter can be your best friend in making sure you get it all right every time.

Light meters come in two main varieties – handheld and hotshoe-mounted. In general, handheld meters are the premium option, with cutting-edge technology and extra functions like flash measurement, touchscreens and wireless triggering of compatible flash remotes. Most meters are battery powered, but there are also battery-free analogue meters available, which can be tremendously handy if you don’t fancy the idea of yet another device you need to remember to charge. Hotshoe-mounted meters tend to be simpler and more affordable.

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As already noted, absorption depends upon the state of an objects electrons. All electrons are known to vibrate at specific frequencies, what is commonly known as their natural frequency. When light, in the form of photons, interacts with an atom with the same natural frequency, the electrons of that atom will become excited and set into a natural vibrational motion. During this vibration, the electrons of the atom interact with neighboring atoms in such a way as to convert this vibrational energy into thermal energy. Subsequently, the light energy is not to be seen again, hence why absorption is differentiated from reflection and transmission. And since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.

By relying on this method, physicists are able to determine the properties and material composition of an object by seeing which frequencies of light it is able to absorb. Whereas some materials are opaque to some wavelengths of light, they transparent to others. Wood, for example, is opaque to all forms of visible light. Glass and water, on the other hand, are opaque to ultraviolet light, but transparent to visible light.

This makes it much more difficult to get well-exposed results out of a camera that is otherwise perfectly functional. Getting a hotshoe-mounted or handheld light meter can be a more cost-effective way to keep the camera running than taking it down to the repair shop. Light meters are also handy if you’re interesting in conducting photographic experiments such as building your own pinhole camera.