Red, Green, or Blue

If you have an indicator that tells you a machine is powered on normally, do you want it to be Red, Green, Yellow, or Blue?

I think of

  • Red as an error or serious warning.
  • Green as go or good
  • Yellow as warning or alert indicating an abnormal state
  • Blue as neutral (no specific meaning)

What do you think?


Red = bad/warning/error (this is why GM dashes in the 90s drove me crazy with their red backlights!)
Green = Good
Yellow/Orange/Amber = less bad red, less good green
Blue, as it was a new color for LEDs in my lifetime and therefore became chic = better shade of green (often upheld by e.g. networkng equipment having their highest negotiated speed on a port being blue, slower being green, slower still being orange/amber/yellow)


I blame submarine movies and the need to preserve night vision :crazy_face:

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Green = Ready / Operating
Yellow = Warning - Attention required
RED = Inoperable / Error


We do have another state that might be restricted to yellow - That is flashing.

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While I typically agree with the standard Red/Yellow/Green logic - we should ask people who are color deficient whether they can distinguish between Red and Green. If not, then we should use Green/good and Yellow as the warning/error.


What about a flashing color? Why not follow the hundreds of thousands traffic lights installed around the country. For the most part, these interlocks will not be the primary interface with any equipment.

Outside of showing the Interlock is powered and being connected to the LAN, what will these lights convey? Following standard Ethernet adapter/switch indicators is probably something to consider. Power, Physical connection to the LAN, intermittent communication, and error.

Currently, most of these devices are not seen by the users.

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Green sort of suggests a machine is “safe,” which it decidedly is not if it’s running. Say someone leaves the jointer running. Woodshop is noisy and it’s hard if not impossible to hear it. They pull the guard back to check the blades…

The lights should indicate that caution is warranted and a green light ain’t it.

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The automotive lift interlock has a multicolor light on it,. I assume that’s the inspiration for the post.

The biggest complaint I have with that light is that it’s difficult to see in the ambient lighting. Whatever light is used really needs to be tried in the brightest area of the space to make sure it’s visible. I assume the existing system was developed in an office or conference room with much dimmer lights than the main shop, then the interlock was mounted at eye level on the lift so you have to look at the light from the side, which probably makes it even less visible than normal.

Otherwise, whatever colors are chosen, labeling them on the box itself would go a long way to eliminating confusion. Realistically, people are probably only going to look at the light if the box isn’t working, so a blink pattern with some basic information might be nice, as long as the key is written down nearby.

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I don’t know exactly what we’re building here, but no reason to limit flashing to yellow. Steady light vs. flashing light vs. flashing lights in a sequence is a popular way of conveying multiple messages/states with limited color/positional broadcasters. Flashing green could mean something different than steady green. Short short short long flash of green, something different still, etc.

No real need to ask, in my opinion. We should really just assume accommodations would be welcome for the the ~4% of us who are color detection deficient and work to make those accommodations an asset for all of us. An example of this is the “stop light order”. Top light is always red. Amber is always center. Green is always bottom. Not sure where blue goes in this scenario, since there’s not a “more bottom”. This could be supplemented by signage (e.g. stop sign next to the red, caution triangle next to the amber, check mark next to the green, double check next to the blue).

I see Sawstop already uses the on/off/blinking fast/blinking slow method…

What do these interlocks do except control power to a tool? Knowing if the interlock is functioning properly on the network, and if a user has been allowed access to a machine is all they normally do.

When I am thinking power only, I have various devices that are Red, Green, Blue or Yellow and all can indicate that power is flowing (plugged in), or that the device is on. I don’t only associate a specific color with a status, I have to look at the device, and what options are there.

I didn’t see that this was an interlock question.

When looking at making a new device (switch), I would think…

No light is that there is no power
Red is that it has power, but not operational
Green that has power, and can be operated.

I see the SawStop option as specific because the machine has circuitry to detect different states.

Now, if this is a new switch could access some external data to determine current machine abilities…

Yellow could be invoked and flashing yellow to indicate not fully functional, but could be used.
Red could be flashing, and indicate that power is on to the machine, but do not use.

Other than having power, I’m not sure of a use for blue.

And all of this is dependent on the defining data being valid and current. If I get accustomed to a machine being Green light (fully operational), I am building in to the expectation that there are no problems.

As of now, any time I activate a machine, I have to consider that there might be value in testing it to be sure it is trim.

These are just interlocks. The user will be using the power switch that ships with the machine. They are not doing anything but allowing power to the machine. The only time a user will even look at them is if they can’t badge in for some reason. The maintenance team might want more info, thus would care about the indicator lights.