Traffic lights are almost great
Posted: October 31, 2011 Filed under: Uncategorized | Tags: real businesses, visualisation 11 CommentsI 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:
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.
magic dashboards 
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.
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.
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.
http://optional.is/required/2011/06/20/accessible-color-swatches/
Thanks Brian, that’s very helpful. I’m enjoying the rest of your blog, as well.
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:
http://www.yankodesign.com/2010/06/09/re-learning-the-traffic-lights/
Some people will already associate the triangle and square with ‘play’ and ‘stop’, which helps. I think this could work on a dashboard.
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.
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.
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.
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.
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.
[…] 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. […]