#!/usr/bin/env python2.7  
# script by Alex Eames http://RasPi.tv  
#http://RasPi.tv/2013/how-to-use-soft-pwm-in-rpi-gpio-pt-2-led-dimming-and-motor-speed-control  
# Using PWM with RPi.GPIO pt 2 - requires RPi.GPIO 0.5.2a or higher  
  
import RPi.GPIO as GPIO # always needed with RPi.GPIO  
from time import sleep  # pull in the sleep function from time module  
  
GPIO.setmode(GPIO.BCM)  # choose BCM or BOARD numbering schemes. I use BCM  
  
GPIO.setup(25, GPIO.OUT)# set GPIO 25 as output for white led  
GPIO.setup(24, GPIO.OUT)# set GPIO 24 as output for red led  
  
white = GPIO.PWM(24, 100)      # create object red for PWM on port 24 at 100 Hertz  
  
white.start(100)              # start white led on 0 percent duty cycle (off)  
  
# now the fun starts, we'll vary the duty cycle to   
# dim/brighten the leds, so one is bright while the other is dim  
  
pause_time = 0.05           # you can change this to slow down/speed up  
  
  
try:  
    while True:  
        for i in range(20,101,5):      # 101 because it stops when it finishes 100  
            white.ChangeDutyCycle(i)  
            sleep(pause_time)
            #sleep(5)  
        for i in range(100,20,-5):      # from 100 to zero in steps of -1  
            white.ChangeDutyCycle(i)  
            sleep(pause_time)  
  
  
except KeyboardInterrupt:  
    white.stop()            # stop the white PWM output  
    GPIO.cleanup()          # clean up GPIO on CTRL+C exit 

#!/usr/bin/env python2.7  
# script by Alex Eames http://RasPi.tv  
#http://RasPi.tv/2013/how-to-use-soft-pwm-in-rpi-gpio-pt-2-led-dimming-and-motor-speed-control  
# Using PWM with RPi.GPIO pt 2 - requires RPi.GPIO 0.5.2a or higher  
  
import RPi.GPIO as GPIO # always needed with RPi.GPIO  
from time import sleep  # pull in the sleep function from time module  
  
GPIO.setmode(GPIO.BCM)  # choose BCM or BOARD numbering schemes. I use BCM  
  
GPIO.setup(25, GPIO.OUT)# set GPIO 25 as output for white led  
GPIO.setup(24, GPIO.OUT)# set GPIO 24 as output for red led  
  
white = GPIO.PWM(24, 100)      # create object red for PWM on port 24 at 100 Hertz  
  
white.start(100)              # start white led on 0 percent duty cycle (off)  
  
# now the fun starts, we'll vary the duty cycle to   
# dim/brighten the leds, so one is bright while the other is dim  
  
pause_time = 0.05           # you can change this to slow down/speed up  
  
  
try:  
    while True:  
        for i in range(15,101,5):      # 101 because it stops when it finishes 100  
            white.ChangeDutyCycle(i)  
            sleep(pause_time)
            #sleep(5)  
        for i in range(100,15,-5):      # from 100 to zero in steps of -1  
            white.ChangeDutyCycle(i)  
            sleep(pause_time)  
  
  
except KeyboardInterrupt:  
    white.stop()            # stop the white PWM output  
    GPIO.cleanup()          # clean up GPIO on CTRL+C exit 

change lower bound to 15%