Can lack of sunlight can affect your mood and wellbeing? That's a good topic for this year's Leaving Cert Computer Science Coursework.
Do I have to use an external sensor?
You can of course use the internal light sensor. I'm showing an external analogue sensor here because if you can use that, you can substitute it with any other sensor eg. sound, temperature, magnetometer, flex sensor.
Analogue Sensor to Micro:bit
Micro:bit Serial Graph
Micro:bit Serial to USB
Thonny Simple Read from Serial USB
Removing junk data & validation
Saving to CSV
Graphing in Matplotlib
Prediction using numpy