Types of Incandescent Lighting Fixtures
The Fresnel (pronounced fre nel’) is one of the most flexible fixtures to work with, being designed to create a relatively even field of light with adjustable intensity and field size. The light is named for its Fresnel lens, which bends the diverging rays of light emitted by the bulb into a controlled beam of light.
The Fresnel lens, nowadays, is still the best tool for condensing light. These lenses have similar characteristics to standard plano-convex lenses, maintaining the basic working principle: bending the diverging rays of light emitted by the bulb into a controlled beam of light, but the Fresnel’s design compresses the convex curve into jagged steps, making it lighter and thinner so that it retains less heat. The lenses can be easily recognized by the circular rings on the glass. These rings act to reflect and refract rays of light so that they travel in parallel lines, increasing the efficiency of the light and producing cleaner-edged shadows.
Equally important, the fixture uses a spherical reflector. Because the bulb is at the focal point of the spherical reflector, light rays coming from the back of the bulb are reflected straight back through the bulb (not directly out the front of the fixture, as in a parabolic reflector). All light therefore emanates from a single point within the fixture (the bulb), which is what allows the Fresnel lens to control the beam so cleanly.
Inside the housing, the globe and spherical reflector are mounted together and can be moved toward or away from the lens by an exterior adjustment knob. The adjustable focus makes it quick and easy to obtain the desired intensity or beam width. A Fresnel light is at the flood position when the bulb is moved closest to the lens, increasing the spread of the beam and decreasing its intensity. Moving the globe and reflector away from the lens, spots the beam, making it narrower and more intense. A lamp in a flood position gives harder light than when it is spotted. In full spot position, rays from the Fresnel travel more nearly parallel, and some converge slightly and cross one another. This creates fuzziness to any shadow cast from an object.
The overall construction of the fixture is using a series of aluminum extrusions and aluminum castings for the outside of the fixture. The reason for this is to dissipate the heat that comes from the light bulb inside the fixture as quick as possible to the external of the fixture so that it can be released into the ambient temperature than by keeping the best operating temperature inside the fixture which is crucial to maintain lamp life. So the design of the fixture thermally helps increase the lamp life of the bulb itself. Secondly, when it is time to wrap, and you turn off the fixture, you want the least amount of time that's needed for the fixture to cool down and that is done again because of all the extrusions techniques and the actual design of the fixture itself.
In recent years, Fresnels become very popular with cinematographers and gaffers. Fresnel lights create reasonably even illumination across the beam of light it forms. This type of fixtures can find many practical uses in studios, location shots, for talents, food and products, to light background elements or as simple accent lights.
Open lights – also known as open face lights, open reflector light, or open bulb lights-are those instruments that do not have any lenses. They are generally slightly brighter per watt and less heavy-duty than a Fresnel spotlight of the same wattage, but the beam is not focused so they are far less controllable.
Open-Face fixtures, like Cinelight Redhead 800W or Blondie 2k, use a double-ended lamp. They have a round face and an adjustable reflector for flood / spot control and come with barn doors and a scrim set. Compared to a Fresnel, the flood / spot mechanism is very unrefined. The mechanism changes the globe's position relative to the reflector. When the globe is close to the reflector, the reflector sends out a wide beam; when the globe is pulled away from the reflector; it reflects more of rays in a narrower beam. Because light emanates from both the bulb and the surface of the silver reflector, open face lights tend to spill light everywhere and this makes them good to be use as a fill light. They are lightweight and durable, with a relatively high intensity per watt. These lights are valued for their high output and small size.
Open face prime fixtures are very good in small rooms and often bounced into a white surface such as foamcore to create soft light. These instruments can be handy for lighting elements of the background set. To be used for lighting actors, a medium to heavy diffusion is needed to take the garish curse off the light.
The PAR lights (which stands for Parabolic Aluminized Reflector) are popular because they put out a lot of light per watt, more than any other incandescent fixture. These lights are also referred to as sealed beam lamps, because the PAR lamp itself includes all the most important parts of a light: the globe, lens, and reflector are one permanently sealed unit, like a car headlight.
PAR lights need separate lenses in front of the fixture; they drop into the front to spread the beam field from a very wide, less intense beam to a narrow intense beam.
These fixtures can be used to light background elements, diffused or bounced into a white sheet for soft fill to light talents (PAR lamps are usually too hard sources for lighting faces). They are often used to light large spaces at night because these lights became a favorite lamp for situations requiring a far reaching, punching beam like street scenes at night.
Soft-lights, as their name implies, are open reflector lights that create a semi broad source. They are designed to produce soft light with less-defined shadows. These boxlike fixtures vary in size and light power over a wide range of luminaries. Some gaffers build their own soft lights to feet the particular needs of size and shape.
The quartz bulbs are not visible. Light from the quartz bulbs is diffused by being bounced off the curved, white surface at the back of the housing. None of the light reaches the subject directly. Most are rigid and large; they are confined to soundstage use, where daily storage and transport on location trucks are no problem. Because it is indirect and exits through a relatively large aperture, the resulting light is soft and has a wide, even, uncontrolled spread.
Because soft lights use indirect light, they produce far less light per watt than Fresnels. Most soft lights have multiple globes, each switched individually, making it easy to increase or reduce the light’s intensity.