Set initial startup background brightness depending on daytime

Basic idea:

1. Save configuration file /opt/.time_brightness_values:

   {
     "5,7": 0.25,
     "8,16": 0.50,
     "17,22": 0.75
   }
   

   Pay attention to quoted values and commas. First column with quoted values represents hour range in 24 hour format, the second column is percentage. For example, if you booted from 5 to 7 o'clock your brightness would be set to 25 percent. If you booted from 8 to 16 o'clock, it would be 50 percent.

2. Save the script below as /opt/set_timed_brightness.py

   #!/usr/bin/env python3
   from __future__ import print_function
   from collections import OrderedDict
   import json
   import time
   import sys
   import os
   
   def read_config():
       dir = '/opt'
       filename = '.time_brightness_values'
       conf_file = os.path.join(dir,filename)
       brightness = None
       with open(conf_file) as f:
            try:
                 data = json.load(f)
                 data = OrderedDict(sorted(data.items()))
            except Exception as e:
                 print(e)
                 sys.exit(1)
            else:
                 keys = [ key.split(',') for key,value in data.items()]
                 keys.sort()
   
                 hour =  time.localtime().tm_hour
                 for key in keys:
                     if int(key[0]) <= hour and int(key[1]) >= hour:
                        brightness = data[','.join(key)]  
   
       return brightness
   
   def set_percentage(pcent):
       dir = os.listdir('/sys/class/backlight')
       dev = os.path.join('/sys/class/backlight',dir[0])   
   
       max = None
       with open(os.path.join(dev,'max_brightness')) as f:
           max = f.readline().strip()
   
       new = int(float(max)*pcent)
       new = str(new)
       with open(os.path.join(dev,'brightness'),'w') as f:
            f.write(new)
   
   def main():
       percentage = read_config()
       if percentage:
           set_percentage(percentage)
   
   
   if __name__ == '__main__':
       main()
   

3. Set greeter-setup-script=/opt/set_timed_brightness.py in the /etc/lightdm/lightdm.conf file. The greeter setup script runs as root and once your system gets up to the login screen, the script will run and set the brightness you need.

4. As far as waking up from suspend goes, create /etc/pm/sleep.d/set_timed_brightness.sh:

   #!/bin/bash
   
   case "${1}" in
           resume|thaw) python3 /opt/set_timed_brightness.py
       ;;
   esac
   

Remember: all the standard rules apply, the scripts must be made executable with chmod +x, naming and calls to each file have to be consistent.