Yeah, so, I’ve been completely ignoring the lighting categories on this site.

Sorry about that.

I guess that I don’t think as deeply about lighting as I do about audio, which is kind of a shame. Lighting is a tremendously fun art and science of its own, and I really enjoy it. I guess that, when compared with audio, I handle the lighting end of things “on autopilot” a lot of the time.

Stage lighting deserves more than that, though. It’s a crucial component of giving an audience what Cliff Bleszinski would call “The Fun.” Part of bringing “The Fun” with (and to) a light rig is to use atmospheric effects – you know, fog and haze. If you’re just starting out, though, it may not exactly be clear that’s there’s a distinction between fog and haze.

HA! Not exactly CLEAR! We’re talking about atmospheric effects and I said that things might not be clear! BaHAHAhaHAHha *snerk* HA *cough*.

I’m WITTY.

Anyway.

Fog and haze aren’t technically the same thing. You can sometimes substitute fog for haze, but going in the other direction isn’t really possible.

Here’s why.

Distribution

In my experience, the fundamental difference between fog and haze is that of their distribution through the room. Yes, the respective chemical compositions of different “fuels” for these effects may differ, and that difference may be profound. However, whatever it is that makes up fog or haze fluid is not always the primary determinant of what you’re going to get.

As a case in point, consider a particular hazer that I own. This hazer uses a water-based fluid that passes through a heating block. The heating block transfers thermal energy to the fluid, and the fluid then vaporizes. The vapor is then propelled away from the unit by an integrated fan.

If you shut the fan off, you have a fogger.

Sure, the fogger has a special talent. It can run continuously without a reheat cycle, which is neat, but it’s still just a fogger with a fan. The fluid formulation might be just different enough to affect hang-time and vaporization characteristics, but it’s still basically fog fluid. In this particular case, you can put the “fuel” in a regular fogger and the machine will, you know, fog.

Fog and haze fluids are NOT always interchangeable in this way. Putting the wrong juice in an atmospheric effects unit can wreck the machine, cause you to get serious burns, start a fire, cause the fluid to break down into dangerous chemicals, and just generally screw up your day. If you experiment, experiment wisely – and at your own risk. DON’T BLAME ME IF YOU RUIN YOUR LIFE.

Okay.

So, what kind of distribution makes fog, and what kind of distribution makes haze?

Fog is characterized by a distribution that is non-uniform and chaotic for a large percentage of the effect’s “hang time.” Haze is characterized by a distribution that is much more uniform and stable throughout it’s entire hang time.

What this means is that fog, as a general rule, tends to be generated as a clumpy cloud that visibly wisps and swirls with air currents. In the room, the density of the cloud can vary greatly from one point in space to the next. As the fog disperses, the cloud’s “point to point” density becomes more and more uniform.

In contrast, haze is generated specifically to be as uniformly distributed as possible. Any “cloud” characteristics should smooth out as quickly as possible – ideally, before the audience notices anything. Further, interaction with air currents should be as minimally visible as possible. As the haze dissipates, its distribution throughout the room should remain uniform. (In other words, the overall haze density in the room should be essentially the same everywhere, with the density dropping at the same rate at all physical points.)

The reason that you can use fog for haze, but not the reverse, is because non-uniform atmospheric effects naturally become uniform over time. On the flipside, atmospheric effects that start out with a very even distribution won’t get clumpy without a lot of work. It’s a one way street where you can start at the “fog” end and arrive at haze, but you can’t travel in the other direction.

Application

The distribution characteristics that I outlined above are what make fog and haze appropriate for different applications.

In general, fog is a relatively short-lived effect that is meant to be visible in and of itself. Haze, on the other hand, is meant to be a long-lived effect that is, itself, invisible.

Fog is meant to look like something. Whether it’s a plume of steam, magical smoke, or eerie mist, fog’s primary purpose is to be a relatively opaque, visible effect. Because fog – like haze – causes light scattering, it also has the cool side-effect of making light-beams visible. This side-effect, coupled with fog machines being traditionally cheap(er) and easy to find, means that there are lots of people who use fog primarily to make light shows more exciting. The uneven initial distribution is just shrugged off.

Haze, on the other hand, is specifically meant to NOT look like anything at all. “Ideal” haze is meant to be invisible until a light beam passes through it, and even then, the point is to see the light and not the stuff floating in the air. Haze is used to let lighting designers make the show more exciting WITHOUT having to deal with the initial clumping and cloudiness of fog.

In certain cases, these different characteristics are used together in complementary ways. For instance, haze might be used throughout a show for the regular lights, but a “liquid sky” effect might be desired at certain points. “Liquid sky” is a laser effect that relies on uneven distribution of atmospheric particles to create a stylized cloudscape. Since haze is so uniform, it isn’t much good for making a liquid sky. As such, fog would be generated only for the parts of the show where the sky effect is needed, with the haze running continuously throughout.

Clear enough? (Oh geeze, the puns…)