In my office there is an air conditioning unit that has a knob that adjusts the temperature with a grayscale bar with the shades getting darker from left to right above it but no other indication (such as numbers, a snowflake, etc). Sort of like this image:

enter image description here

This is very confusing to me. Typically I would think that temperature indicators would go from left to right (cold -> warm). But what if this isn't temperature but rather intensity where a higher intensity blast of air would result in colder temperatures? (off -> full blast)

Is white cold and black warm? Or white low intensity and black high intensity? Is it a badly designed indicator or are my intuitions off?

Bonus: What would be an idea for a better but just as minimalist design? How universal is this current design? Would snowflakes make more sense and how well understood would that be in climates with no snow? I don't think numbers would help unless they are associated with temperatures explicitly.

I took a photo of the knob. It doesn't look exactly like my illustration (in my defense it was dark inside the grid :-P )

enter image description here

  • 1
    A real image will help. Jun 8, 2015 at 7:29
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    clearly not the best design, though I have seen lots of air conditioning units like this and it is the remote that displays more details such as numbers for temperature and snowflakes etc. Does it not have a remote? It's even more confusing as air conditioning units as you turn them 'up' i.e. power, you actually make them colder so in theory the bar going further and further towards the black must mean it is making colder and colder air. Weird
    – Chris
    Jun 8, 2015 at 7:54
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    I'm having a similar problem with my fridge at the moment. Does '1' mean a setting of 1 degree or level 1 intensity? If I want it to be at its coldest do I need 1 or 5? Better just leave it at 3 to be on the safe side. Jun 8, 2015 at 14:31
  • 8
    It's AC controller. I've never seen any single one work properly anyway, it really has only 2 settings, "Arctic" and "Death Valley".
    – Agent_L
    Jun 8, 2015 at 17:10
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    Is it possible that the knob had the classic red-blue color scheme once upon a time, but the color was sun-bleached since then?
    – svick
    Jun 8, 2015 at 17:13

6 Answers 6


Yes, it's bad design for its lack of signifiers (signs in the world that offer guidance).

  • You can't distinguish what device it belongs to by just looking at it.
  • You can't know its purpose without trying it out.
  • It does't show its state clearly. Could we establish a clear relationship between one state and one temperature easily and consistently? I don't think so.

Adding one or more signifiers will help to improve it, some examples (more or less ordered from best to worst based on my preference):

  • Numbers: representing temperature or "level of intensity" (the last one will also need a complementary signifier to know if the bigger number, the higher or lower temperature.)
  • "Cooler" and "Warmer" labels in each corresponding extreme. Depending on the amount of states and if they really make a difference in the functionality you could add other intermediate states.
  • Cooler-Warmer symbols. A sun, curvy lines (as wind), classic snow icon.
  • Use of colors (warm and cold colors). Luckily for this case, blue color blindness affect less people than red and green color blindness.
  • 5
    +1 for stating that just numbers for intensity are not enough. I'm always confused by refrigerators that have number settings - I have to try it out to see which direction causes it to cycle on or off.
    – Random832
    Jun 8, 2015 at 12:45

Yes, Use of grey scale for depicting temperature is not at all a good idea.

The photograph shows clearly the change in intensity as the knob moves from white to grey. But it doesn't communicate the purpose of intensity, specially knowing that this knob is for adjusting the temperature, I think they got it all wrong.

A simple color depiction would have solved the problem.

A minimalist approach is to use colors users (by and large) can associate with temperature. Its blue for cold and red for hot.

enter image description here

Some examples of cool and warm color will help:

enter image description here

  • 8
    Unless you're into astronomy, where red stars are the cool ones, and blue/violet ones are really hot. Or metalworking...
    – jamesqf
    Jun 8, 2015 at 17:32
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    @jamesqf Astronomer should be really afraid of air conditioners then. I wouldn't dare approaching a device which blasts air at temperatures between 2000K and 30000K. Jun 9, 2015 at 17:12

Combining the answer by @pzw and the original knop, referring a bit to @AntonioMarquis : we don't have to mix the colors to get the idea of 'temparature' across. These knobs might, indeed, be hiding in dark places, so let's keep a fair amount of contrast in the graphics. Just adding some (solid) color would do the trick. I also chose light blue instead of saturated blue, to keep good contrast between red and blue (also because of color blind people).

example of knob using two colors


It could be a good design. A lot of times users would think an A/C temperature needed to be a specific number. The truth is that the A/C should be set to something comfortable.

In an office environment this leads to people "fighting" over the A/C setting. It also leads people to set the setting when they are not supposed to. For example setting a dial to full blue because they are hot.

By using that dial and representation, you discourage users for tinkering with it, because, frankly, there is no way to tell (at a glance) rather your setting it cooler or warmer. A Facilities guy could know "warm is gray" but the average user wouldn't have a clue.

That said, I think there are much better options for climate control then confusing knobs. But this could be a good design depending on goals. If you need a temperature knob, that discourages people from messing with it, while being cheap and in the open, this should do the trick.

I suppose there is also the possibility that this is not a temperature knob and is something like fan speed, that has little baring on temperature. Still, I would say that it's generally a bad design unless you were specifically trying to discourage turning the knob frequently.

  • "A Facilities guy could know "warm is gray" but the average user wouldn't have a clue" Wow you found the one situation where a bad ui is a good thing.
    – Navin
    Jun 9, 2015 at 8:06
  • It's important to remember that a good UI doesn't mean easy to use. A good UI meets the goals of the project. My contrived example could be a project goal that would result in a hard to understand setup. The only other one I could think of is "super cheap" 1 color is cheaper then 2 or 3 but that doesn't explain why there is no sun and snow flake or numbers or H and C or what ever.
    – coteyr
    Jun 9, 2015 at 15:59
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    In that case it would be better to remove the knob altogether and make it screwdriver-adjustable. Jun 9, 2015 at 17:15
  • Except then you have to carry a tool.
    – coteyr
    Jun 9, 2015 at 17:51
  • mscdirect.com/product/details/… requires a key. I'm just saying that if the goal is super cheap, no extra keys, and confusing to the normal user, then this is a good UI. Another example, "We want to use the same knob on fans, pressure valves, volume knobs and anything else we can think of and we want to include it on our "budget" lines so you have to have a production cost of less then $0.05." My point is that a good UI meets the projects goals, even if the goals do not include ease of use.
    – coteyr
    Jun 9, 2015 at 17:56

One-word answer would be Yes.

This is definitely not the right way of depicting information and it is open to perception.

When a system is designed, you need to consider user's mental model. So you are right in perceiving the bar in different ways. You approach the design with your preconceived notions, or mental model which may or may not be exactly how the system works.

Thinking minimally, the shades of blue to red should universally depict, coldness and hotness respectively. However, that is not enough. You need to think about people who have specific color blindness. So there should be labels denoting the end of the scales as well. It is a Myth that just icons enhance usability, so a snowflake alone can not save you either. Just minimalisation should not hamper the user experience.


Use grey scale to show light and the tertiary colors for temperature. A Tertiary Color is a color made by mixing either one primary color with one secondary color, or two secondary colors, in a given color space such as RGB and CMYK (more modern) or RYB (traditional).

  • 3
    I don't understand what you mean.
    – giraff
    Jun 8, 2015 at 19:05
  • A Tertiary Color is a color made by mixing either one primary color with one secondary color, or two secondary colors, in a given color space such as RGB and CMYK (more modern) or RYB (traditional). Jun 8, 2015 at 19:17
  • 1
    Welcome to UX.stackexchange. Could you elaborate on your answer? As it is it functions more as a comment than a free-standing answer.
    – Mayo
    Jun 8, 2015 at 20:37

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