Light is invisible until it hits something. We do not see rays of sunlight except, perhaps, after a rainstorm when the air is full of mist. A foggy night will show off the headlights of an oncoming car or beams of moonlight. The water particulates in the air give life and presence to light in a way that is simply not possible without them. This is equally true on stages.
After exploring leaves and trees and clouds we moved on to abstract patterns. While those essays focused on types of pattern and some basic issues of focus they did not look at how to get the most impact out of your template choices. Haze and fog are particularly effective tools to maximize the effect of your templates.
Because atmospherics allow us to better see the physical beams of light, it means that the light itself takes on a greater visual role. We can see, through the use of haze, where the light comes from. The volume of the performance space is brought to the audience’s attention in a way that it is not otherwise. Because the light is visible before it hits performer or scenery, the world of the show becomes larger than any of those elements. Light can make the world bigger.
We know from our exploration of backlight that a light pointed more in the direction of the viewer will be more present than a light coming from their angle of view. Adding haze, or other atmospherics, will amplify this. How much of an atmospheric effect you use will be guided by the needs of a production. A rock concert will probably demand a heavy use of haze to fill the air thickly. A comedic play, on the other hand, will demand a much lighter touch, perhaps with haze running intermittently on an effect to give just enough presence to the air to make it filled with light.

What kind of atmospheric to use is a critical design decision. The two most common forms are haze and fog. Both of these are chemical based solutions which are heated and then pumped out onto the stage. In addition to these there you have water, dry ice, and smoke.
Haze is probably the most common and produces a thin mist which fills the air. It can range from subtle to obvious depending upon how much is used. Rather simple to control, this is a solution favored by many designers for that fact. A good hazer will fill a performance space quickly and evenly leaving a beautiful mist hanging in the air. One of the greatest benefits of haze is that the particulates hang in the air much longer than natural solutions like water. While it used to be less than healthy, current haze juices are safe in the human respiratory system under reasonable conditions.
Fog operates like haze in that it is a chemical solution. It tends to be very thick and used for smoke effects in more realistic situations and as broad and powerful statements in more abstract spaces. It is rarely if ever subtle. Because fog is so thick it really shows off the beams of light in an architectural manner. Form and color become quite prominent and as such one’s choice of template is critical. Because it is thicker than haze it can be a little more risky for those breathing it in, but is generally safe under reasonable conditions.
Misting systems are especially popular in situations like opera houses which do not allow chemical based atmospherics. This is a water based solution which uses high pressure misting hoses to fill the air with water. While the effect is quite beautiful it has several inherent drawbacks. First, the particulates do not stay in the air. As such the system must run continuously to maintain the effect. This, then, amplifies the second problem which is that water is wet and can cause damage to scenery and costumes. Not to mention wet and slippery floors!
Dry ice is an atmospheric effect which, rather than filling the air, rides close to the ground. Thus its impact on light and templates is often minimal. Because it is so heavy, it can be used to cascade down walls or through the air. Under such conditions it can act as an atmospheric for the purposes of showing of templates quite nicely. Because it is frozen CO2 it poses no health risks. Despite this reality, it is one of the most common effects to induce psychosomatic bouts of coughing.
Smoke would probably be the last atmospherics to consider. Typically an after effect of pyrotechnics, smoke works beautifully to fill a room with particulates against which light might shine. Of course, unless you are doing a big pyro show or a fire ballet, chances are the presence of smoke will be intermittent at best.

The design needs of the show, and sometimes contractual needs of the performers, will determine what solutions are best for you. Each of these atmospherics create beautiful effects of light. Under the right conditions these tools assist in creating beauty and transcend their role as effects. Anyone can flood a room with fog and haze and turn on the backlight templates. Balancing this with the needs of the show to create a thing of beauty takes careful consideration and finesse.
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