Traffic lights are almost great

I use red/green signals in dashboards all the time. Everyone knows the red/amber/green code, so they instantly convey a rough and ready view of business performance. If there is a lot of red, there is a problem; everything green, no problem.
They come with one major catch, though, which usually gets forgotten. About 7% of men are red/green colourblind. To them, a traffic light looks more like this:

and red and green bits of the dashboard are indistinguishable.

What to do?

I’ve never solved this to my satisfaction. Most of the time I use pattern as well as colour – e.g. red lines are dashed while green are solid. This is a bit of a hack, and doesn’t have the same easy accessibility or the same emotional impact for dashboard users as red/green does.

I’d love a better solution. If you have ideas, please let me know in the comments.


11 Comments on “Traffic lights are almost great”

  1. Simon Wistow says:

    I’m one of the 7% and I have no problems with those examples – I only really have a problem in much more difficult conditions. My favourite example was the power light on the stereo in my bedroom when I was younger – if I woke up in the night I couldn’t tell if the small LED 6ft was red or green but during the day I had no problem.

    The US Navy uses the Farnsworth Lantern Test rather than the Ishihara Dots test to detect colour blindness which apparently allows a further 30% of people with only a mild condition to pass and I suspect even their standards are more rigourous than you’d need for a dashboard so I suspect it may not be as big of a problem as you worry.

  2. magicdashes says:

    That’s good to know. It never occurred to me this would even be a meaningful problem until a couple of years ago, when it turned out that the reason the guy in charge of the company absolutely *hated* our main dashboard was because it was totally based on red/green signals.

    In the US Navy it must be even more important to have redundant info in red/green signals, especially if they allow people with mild colour blindness. I wonder how they get round it?
    I also found out researching this that colour blind people in Singapore, Romania, and Turkey are apparently banned from driving. Seems excessive.

  3. Brian Suda says:

    I have been experimenting with a “safe” colour pallet. It means that I have a short-list of goto colours that will work in all these different circumstances, even a black and white print out.

  4. As Brian said, the solution board-game designers tend to use is to distinguish between things using symbols or shapes as well as colour. This solution has been proposed for real traffic lights too:

    Some people will already associate the triangle and square with ‘play’ and ‘stop’, which helps. I think this could work on a dashboard.

  5. TeamCity’s tray notifier gets around this by having an exclamation mark in the red light, a tick in the green light, etc. This works really well when it is just an icon in the system tray.

  6. Frazer says:

    My firm uses traffic lights in pretty much all of our dashboards – my documents are littered with the damn things. The RED has a sad face etched on top of a red circle, the AMBER a neutral face and the GREEN a smiley one.

    • magicdashes says:

      Wow – does anyone ever use the red light if it’s not only red but also has a sad face?

      In a previous job I used to produce traffic light reports and was all but banned from using amber or red as it made people look bad – the closest I was allowed was a kind of yellowy green which was less green than a proper green light.

      • Jen says:

        It sounds like a pretty dysfunctional organisation that cannot cope with red/amber … unless it was against each person’s name which seems a little harsh!

        Traffic lights are great for instantaneous status but I kind of like things like weather reporting (see the default Jenkins installation) for communicating a bit about how the status has changed over time – sunny means all is good, cloudy means we had some problems recently but they are going away, rain means a temporary blip and thunder means everything is going bad. OK it’s a bit cute, but some metrics do need that extra context… for example if I was Red last week, being amber today is actually a good thing.

        Incidentally, talking of Jenkins it defaults the status indicators to blue not green – I wonder if that is for the colour blind among us.

      • magicdashes says:

        I shouldn’t name names, but it was a huge and otherwise very high-functioning tech company – I think that stuff just creeps in when you have a big company with internal politics. Just brewing a blog post now on KPIs, I should include that as an issue.

        I like the idea of the Jenkins weather display, haven’t seen that. Sparklines in Excel are a slightly more corporate way to do the same thing – point at direction of travel without needing to display exact figures.

  7. […] facts. Ideally there should be a number attached. Don’t use traffic lights if you can possibly avoid it – they’re way too vulnerable to internal politics. […]

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