Fog VS Haze: What’s the difference?!
In this blog, we’re talking about the science and technology of atmospheric effects! This is the first blog in a series about atmospheric effects. In this one, we will define haze effects, review how heated atmosphere effects work, and dive a little into the fluids used to make the effect.
Definitions & Defining the Scope
Vapor-based atmospheric effects are used because they scatter light effectively, this allows a volume of space to be seen. This topic can get confusing without defining some base terminology. Most atmospheric effects are a type of fog. While these effects are often referred to as “smoke”, that is not the case. So what is the difference?
“So the reason that it’s called fog, even if it is a smoke-like effect, is that it’s droplets of liquid in the air. Smoke is dry particles that’s usually made by burning something. And you have dry particles in the air but with fog, it’s liquid droplets. So it can be a thick fog effect that goes away quickly, could be a ground fog effect, it can be a thin fog that lasts a long time, which is typically called haze. But if it’s wet it’s fog and if it’s dry, it’s smoke. At least from my terminology.”
So now you might be saying “This video had haze in the title. Why are you only talking about fog?!” Well that’s because haze is a fog, mist is a fog, fog is a….. well, fog. For the sake of simplicity, when we’re talking about the whole category of vapor effects, we’re going to umbrella all these into the term “atmospheric effects” in the hopes that it makes things clearer.
Lastly, there are also many ways to create atmospheric effects. This video is only going to go over heated effects.
Types of atmospheric effects
The goal of using atmospheric effects is to produce a cloud that our eyes can see or to make light visible in space. Let's go over the different types of looks atmospheric effects make. The TL;DR is, it’s all about vapor size. Our friends at Master FX have a great explanation of this:
Haze
Haze is like the “invisible effect” of the vapor genome. Unlike the other atmospheric effects, it's not meant to be the star of the show but allows the volume of the space to be seen. With haze, you’ll want it to be evenly distributed and last a long time.
So how is this achieved? Haze fluids are designed to atomize into incredibly small droplets that evaporate slowly. Since the particles are so small AND because they evaporate slowly, this allows them to hang in the air for a long time.
“When it comes to haze, you know, the whole goal when Haze was first created was just to see the light beams in the air. So for lighting purposes or photography or video where you just want to see the nice translucent beams or lasers, you know, shining through this light but not necessarily obstructing your view so that’s the whole deal with haze. ”
Fog
Moving our way up in droplet size, we have fog, which there are also a couple of subcategories that we’ll dive into. Fog droplets are bigger than haze droplets and because of this, fog is visible and can show the air currents, for better or worse.
Another quality of note is because the droplet size is larger, fog hangs in the air for shorter periods of time than haze. Fog machines use more fluid compared to a haze machine because of this.
“Fog is going to obscure your vision. So when we want to come up with fog effects, we want the fog to be seen in the air. So whether it’s a low-lying fog where you can see clouds of fog or at a rock show or a theatrical event, where you actually see density in the air, that’s what we classify fog effects.”
Faze
Some popular machines in the market are “Fazers”. You may be able to guess what frankenstein’ed concepts were put together to make this name. Faze machines use fog fluid and fans to make the fog fluid look more haze-like, the effect looks wispy and it’s very easy to see air currents.
Fazers are cheaper to buy in comparison to a proper hazer, but they do have a few drawbacks. Since fog fluid is used, it has all of the drawbacks of fog droplets and none of the strength of haze-size droplets. So you’ll be using more fluid and the “Haze” will not be even.
Low-lying Fog
This effect is generally made by chilling the fog. This can be done in the production of the effect (E.G.- cyro-based machines) or by chilling the heated vapor post expulsion from a hazer. As the name implies, this effect looks like clouds rolling along the ground.
Mist
Mists are the heaviest of all the atmospheric effects. It looks like something in between a drizzle and fog. Since the droplets are so big, they can easily be seen in the air. Also because of the droplet size, they fall out of the air quickly and need to be replenished often.
Heat Effects
Atmospheric effects can be made in a couple of ways: cold stuff (Cryo), violent stuff (Mechanical Mean), and what we’re focusing on, heated effects. If you want us to make a video on other means of making atmospheric effects, let us know in the comments.
Heated systems work by propelling a fluid into a heat exchanger that then vaporizes the fluid. That vapor is then pushed out of the machine and mixed with the air. There are two main types of heated systems: pump-propelled and gas-propelled.
Pump Propelled
Pump-propelled fog machines use a fluid that is composed of a mixture of glycols and water, which is pumped from a reservoir into a heat exchanger. The heat exchanger then vaporizes the fluid, causing it to expand and be forced out the front of the machine where it mixes with cooler air and forms an aerosol of tiny droplets.
Gas Propelled
Gas-propelled fog machines use a non-flammable gas (CO2 or N2) mixed with a mineral oil or glycol-water mixture from an onboard tank to be propelled into a heat exchanger. The amount of fog produced is controlled by a regulator valve on the gas bottle.
Types of Fluids
Let’s talk about the types of fluids that can be used in heated systems. There are 4 main fluids used:
Water
Water mixed with one or more glycols or glycerin
Pure Glycol
Highly refined mineral oil
You may be questioning now “If water is one of the ingredients why would I need any of that other junk in my fluid mix?”. While water is cheap and is not questioned as unhealthy in normal situations, it evaporates quickly and scatters light worse when compared to the other fluids.
To understand the refractive qualities of a substance, we have to talk about the refractive index.
The refractive index is a measure of how much light is bent when it passes through a medium, like air or water. To oversimplify, when light enters a medium, some of the light changes direction. The amount of bending that happens depends on how optically dense that particular substance is.
Higher indexes mean more light bending, which means more scattering of light. For example, air has an index of 1.
Water is 1.33
Propylene glycol is 1.43
Mineral oil is 1.47
Now let’s dive deeper into the two main types of fluids!
Water/Glycol-based Fluids
Water-based fluids are made with a mixture of water and glycol and/or glycerin. Depending on the balance, they are sometimes called “Glycol-Based” fluids, but I have not seen that as often as the “Water-Based” labeling. What’s great about water-based fluids is that compared to water, they evaporate slower, they reflect light better than pure water, and different mixes can have different effects. The main drawback is that the fluids are slippery, if spilled they need to be cleaned carefully to avoid slipping hazards.
Mineral Oils
Mineral oil is a type of fog fluid that has the advantage of never evaporating, creating long-lasting effects. However, it can also leave behind a slippery residue because it never evaporates and can leave a slight oily residue on surfaces. Be prepared for a bit more cleanup compared to water-based fluids. It's a good idea to test a small area before using the fog machine in a larger space.
Hopefully, you have a better understanding of how haze and fog effects work. In our next installment in the series, we’ll dive into the safety considerations you should make when using vapor-based atmospheric effects.
