Why does the else statement still play if the if statement in python for a while loop

I decided to make a mini-game as my 1st program since I am very new to python. The user must enter yes to start the game if you type no the program is supposed to say "bye-bye" and end. if anything else is entered it print "I do not understand bye-bye" However when I enter no it plays the else statement along with what was supposed to play when it enters no. How do I fix this? This is my program (sorry if it's a little long). You can run it and type no to see what I mean.

light_on = False
door_open = False
print('hello')
start = input('Would you like to play a game yes or no ? ').lower() 
if start == 'no':
 print('bye bye')
while start == 'yes':
 print('Type help if you do not know how to play')
 command = input('Command?: ').lower()
 if command == 'help':
   print('''
on = turn light on
off = turn light off
open = open door
close = close door''')
 elif command == 'on':
   if light_on:
     print('The light is already on')
   else:
     light_on = True
     print('The light is bright and warming')
 elif command == 'off':
   if not light_on:
     print('the light is already off')
   else:
     light_on = False
     print('the room is dark and scary')
 elif command == 'open':
   if door_open:
     print('the door is already open!')
   else:
     door_open = True
     print('the hallway is so dark you cannot see')
 elif command == 'close':
   if not door_open:
     print('the door is already closed!')
   else:
     door_open = False
     print('you slammed the door shut')
 elif command == 'quit':
   print('bye bye')
   break
 else:
   print('I do not understand')
else:
  print('I do not understand bye bye')