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Bellis's Law of Control Proximity

Or, "The Light Switch Rule" January 24, 2005

Since moving to a new home a few years ago, I've been busy moving light switches around, so they're on the wall closest to the light they control. That's not too sophisticated, right? Well, I've noticed that the same applies to software controls, even text... put them immediately beside the item they control or refer to.

In my new home I've spent a lot of time fixing light switches. First there was the mystery of several switches with broken knobs. What's that all about? It was too much of a coincidence. Turns out—and the electricians out there will find this all too familiar—one of the prior homeowners must have replaced 3-way switches himself and didn't know how to wire them. So when they failed to function properly, rather than correct the wiring, they simply set one of the two switches to a workable position and broke the handle off!

And then there was the peculiar self-activating rear floodlights. Sometimes I would find that the rear floodlights were on. I'd turn the switch (in the mudroom) off and a few days later they were on again. Well, it turns out that one of the broken-off switch handles was in the master bedroom, at the front (not the rear) of the house. And that broken switch would occasionally get toggled, accidentally, when we were turning on our bedroom lights with the adjacent switch. Since we never know what it actuated, it took a long time to realize it was a 3-way switch with the one in the mudroom, controlling the rear floods! Apparently it was considered helpful to be able to turn off the rear floods from the master bedroom?! Well, with all of the mysteries solved, I then set to work correcting all of the poor positioning of the switches, because you constantly have to ask yourself, what does this switch do? Here were the problems:

  • The switch to the driveway floodlights is in the foyer, not the room nearest the driveway, the garage.
  • The switch to the garage light isn't in the garage, but the next room in, the mudroom.
  • The switch to the driveway motion sensor light isn't in the garage, but in the mudroom.
  • The switch to the basement lights is not at the foot of the stairs but in one of the rooms.

And what does all this have to do with software? I realized amid all this work that it's the same principle with interface controls: put them precisely at the item they control. I have two examples, DreamWeaver and Atomz.

The Reset Image Size Button in Dreamweaver

Before   In the following figure from DW4, the Reset Size button controls the W and H fields, setting them both to the original 100% size of the image.

After  The Macromedia folks realized it should be right at the fields it affects and changed it to an image button in the next version:

The Atomz Options Blurbs

Before   Notice the two check box options. What do they mean?

After   In my own suggestion for an improvement, the text is right with each field. Not my best UI work, but you get the point:


Try this quiz. How would you fix this dialog?

I haven't come across this principle, control proximity, out there in the literature or heuristics much. Does someone else get the credit? Let me know so I can credit the proper source. —


"My interest in usability arose from the pain and tears of patching the wounds of suffering interface designs with the inadequate bandages of help files and user guides." — Daniel Cohen

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