Artificial light sources allow photographers to shot without having to depend on the natural lighting conditions present. Increasing the amount of light present also allows photographers to use lower ISO settings which decreases noise and grain, producing higher quality images.
Continuous Lighting
Continuous lighting remain designed to stay on for long periods. Continuous lighting allows a photographer to see how the light will influence a shot before actually triggering the shutter release. The shot can be carefully composed to produce the exact image desired.
The drawback? Continuous lighting sources tend to be less powerful than flash sources. The photographer may still need to use a higher ISO or slower shutter speed than required with flash photography. Whether this matters depends on the subject being photographed. A slower shutter speed makes little difference when subject that are immobile but may matter with live subject, like small children.
There are various types of continuous lighting sources available. Each has advantages and disadvantages.
Incandescent Light
The original source of artificial light. Incandescent lights work by passing an electric current through a filament that resists the flow of electricity. This resistance causes the filament to heat up. It glows as a result of heating up.
This is the main drawback of using incandescent light sources. They are inefficient when it comes to light production and they produce heat.. Much of the energy is lost as heat instead of producing light. (There is a reason why toasters, electric ranges and electric kilns use this method to produce heat.)
Incandescent lights produce "warm light" meaning they produce light with a yellow or orange cast. The exact color temperature depends on the type of light involved.
Incandescent lights designed for home use have a color temperature around 2800K. Halogen lights have a slightly higher color temperature (3000-3400K).
Halogen lights produce more light and heat than regular household incandescent lights. They require the use of quartz instead of glass to deal with the heat produced by the filament.
Fluorescent Light
Fluorescent lights work by using an electrode to stimulate a small amount of mercury in a sealed tube. This causes some of the mercury to turn into a gas. The electrons flowing through the tube collide with the electrons of the mercury gas. These electrons emit light when they lose the extra energy gained from this collision. The mercury gas primarily produces ultraviolet light.
The inside of the glass tube is covered by a powder that fluoresces (produces light) when exposed to ultraviolet light. The fluorescent coating can be altered to vary the color of light produced. Fluorescent light bulbs typically produce "warm white" light (3000K) or "cool white" light (5000K).
Fluorescent lights are more efficient than incandescent requiring less energy to produce a similar amount of illumination.
The mercury used in fluorescent lights can pose a health hazard if the bulb is broken and there are disposal issues involved in the use of fluorescent lights. They also don't emit light consistently across the entire light spectrum. This can cause a greenish cast when shooting under fluorescent lights. This can also cause certain colors to be rendered inaccurately.
LED Lights
Light Emitting Diodes are the latest edition to the artificial lighting market. LED technology has been around since the 1960's but have not been suitable for producing large amounts of light until fairly recently.
Light Emitting Diodes work by passing a current across a semiconductor. The semiconductor emits light as a result of the electric current. LED lights are more efficient than both incandescent and fluorescent lights. The light produced is a direct result of the electricity supplied to the LED. Very little energy is wasted as heat.
LED lights also offer the advantage of being able to produce a specific wavelength of light. LED lights can produce infrared, ultraviolet or visible light of any color simply by altering the semiconductor used.
The main problem with LED lights right now is price. They cost much more than the alternatives, but this is changing fairly rapidly.
LED lights also struggle to provide light consistently across the light spectrum. Like fluorescent lights, LED lights can produce a color cast or cause colors to be rendered inaccurately.
Even with the drawbacks, LED lights fill a useful roll in photography at present. The very low power use couple with the small size of the diodes makes LED lights well suited for portable light sources. A rechargeable LED light panel can provide light for several hours of constant use and can provide useful amounts of light.
Flash Lighting
Flash lighting produces a bright burst of light that lasts for a short period of time. Flash units require less power overall than consistent lighting. They do require power to be released in more powerful bursts.
Modern electronic flash units work by applying a large voltage charge to ionized xenon gas. The electrons in the xenon atoms get a boost from the charge and then emit light as they lose this extra energy. This is similar to how fluorescent lights work, but the xenon gas produces visible light instead of producing light that is mostly ultraviolet in nature.
Flash units have drawbacks.
Flash units require a burst of high voltage to work correctly. This means storing energy up over time. This makes the flash unit unavailable as a light source while this charge is building.
Flash units can cause red eye when photographing living subjects. This can be addressed using software.
Flash units powerful enough for studio use can also be very expensive. There are inexpensive alternatives, but these have drawbacks as well. The least expensive alternative uses individual flash units. Each unit has to be plugged into a different outlet which can be a problem if multiple lights are desired.
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