Designing a visual indicator here is non-trivial
A charger has at least the following states, and possibly more:
- The charger is not plugged in correctly, or there is no power in the wall socket
- The charger is plugged in correctly but the device is not charging (e.g. faulty cable, device isn't fully plugged in)
- The charger is plugged in correctly and the device is charging
- The charger is plugged in correctly and the device has finished charging
It's difficult to communicate states using just one LED:
- A designer could use flashing or pulsating lights or dim/bright lights to communicate multiple states, but that is not very clear to the user.
- A designer could use symbols (labels are language-specific and the charger needs to be globally understood), but that adds clutter to a small device.
- A designer could use multiple indicators to show plugged in vs charging vs finished, but wall chargers are supposed to be unintrusive and multiple lights start to create visual distraction on the device.
A decision not to include an indicator on the charger can be the result of thoughtful design which incorporates these considerations. By examining the UX goals here, one might posit:
- The user's goal is to charge the phone.
- In order to do that, the user needs to get clear feedback that the charging process has started correctly, and that it has finished. In between these two events, the users needs to be able find out how fully charged the phone is (i.e. progress).
- Rather than provide a tiny indicator on the charger, which creates problems because users might buy 3rd party chargers, charge from laptop, etc. it's better to use the phone itself as the indicator:
- The phone has a large display for communicating start, progress, and end correctly
- It has a speaker for audio feedback
- It knows the user's language and can provide language-specific labeling
- Showing the charging indicator on the phone allows Apple/Samsung/etc to ensure a consistent charging user interface even if users utilize 3rd party or non-conventional chargers.
The phone-based indicator is not perfect. If the phone battery is totally dead, there is no indicator at all since there is no power to the screen (that's one of the reasons phones try to switch themselves off with a tiny reserve amount of power rather than run to zero). If there is a problem with the cable, or charger, or wall power, there is no additional indicator to help users debug what might be wrong.
But rather than cater to these less frequent cases, designers correctly have focused on the majority use case, which then allows them to design chargers which are:
- Unintrusive (no flashing or bright lights)
- Encourage the user to use the phone rather than the charger as an indicator (consistent user interface)
- Unambiguous (no labeling required)
- Clean/minimalist (a design objective for companies like Apple and Samsung).
There are certainly reasons why one should provide visual indications (it provides more information to the user, one should provide feedback on BOTH the charger and the device), but a reasoned compound design tradeoff here has empirically resulted in chargers which favor simplicity and phone-based rather than charger-based design.