I wanted to know for how much time the screen of my laptop(with Ubuntu) was 'ON' for the whole day.
I have used 'uptime -p' but it doesn't work if you turned your system off and then later turned ON for use. Hence, it tells for how long the system(not screen) is running from the last time it was turned ON.
Please suggest if there are any other softwares/desktop-apps also.
There are some tools like links below which you can use to measure Screen Time:
ActivityWatch (Free)
RescueTime (You need to pay)