When it's completely dark, even the lowest brightness setting on an iPhone can be too much. Many iPhone users therefore use special external protection filters to darken the screen, or they jailbreak the device. But that is not necessary at all, because from iOS 8 there is a night mode built into the zoom settings. The function can be activated by clicking three times, but setting the function is not so easy to find.
Steps
Method 1 of 2: Set Night Mode

Step #1. Open Settings app
Tap General, then tap Accessibility.

Step #2. Tap on the 'Zoom' tab

Step 3. Set the zoom area to 'Zoom entire screen'
This way you can apply the night mode filter to the entire screen.

Step #4. Tap on the zoom button to activate the feature
The button will now turn green. It is possible that the zoom function will immediately become visible and that a filter will be applied, but that will not affect the further steps.
If the window is zoomed in and you can't see all the options, tap the screen twice with three fingers at the same time to zoom out again

Step 5. Tap the screen three times with three fingers to enter the zoom preference menu
Tap in quick succession, as it may only register two taps (which zooms you in and out) or nothing.

Step 6. Turn off the zoom itself, unless you do want to zoom
You do this by moving the slider at the bottom of the preference window all the way to the left.
If you see the option 'Hide controller', click on it to hide the controller

Step 7. Tap on 'Choose filter' in the preference menu and then select 'Low light'
Now tap outside the menu to exit the menu.

Step 8. Turn off the 'Night Mode' function again
If you want to turn the setting off again, either disable the 'Zoom' slider in the settings, or select 'None' from the 'Choose filter' menu.
Follow the instructions in the section below to easily activate and deactivate Night Mode
Method 2 of 2: Create a shortcut

Step #1. Go to the 'Settings' app
You can create a shortcut to easily reach the 'low light' filter. Tap General, then Accessibility, then scroll down and tap Accessibility Quick Options.

Step 2. Add zooming by tapping on 'Zoom' option

Step #3. Use the quick option
Now you can toggle night mode on and off by triple clicking the home button.
If you have activated multiple accessibility options, a menu will appear after three clicks. In that case, tap 'Zoom'
Tips
- When zoom mode is activated, you can zoom in and out by double-clicking the window with three fingers. If you accidentally zoom in, you can double-click again with three fingers to zoom out again.
- If the whole screen goes black then you are probably zoomed in too far. Double tap with three fingers to zoom out again.