Code

#!/usr/bin/python3

from tkinter import *
from time import *

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(3,GPIO.OUT)
GPIO.setwarnings(False)
root=Tk()
root.geometry("450x140+100+100")
root.title("Haupemenue")


led_status = "aus"
scale_vorhanden = "nein"
scale_wert = 0
bewaesserung = "True"


def hauptmenue():       #Hauptmenuebuttons erstellen und anordnen
    btn_LED = Button(root, text="LED", command=led)
    btn_LED.place(x=10, y=20, height=100, width=100)

    btn_exit = Button(root, text="Beenden", command=root.destroy)
    btn_exit.place(x=340, y=20, height=100, width=100)
    

def led():          #Button und neues Fenster erstellen
    led=Toplevel()
    led.title("Bewaesserung")
    led.geometry("500x170+100+100")
    lbl_led = Label(led, text="LED AN AUS")
    btn_exit = Button(led, text="Hauptmenue", fg="red",  command=led.destroy)
    btn_exit.place(x=400, y=140, height=30, width=100)
    btn_led = Button(led, text="LED Toggle",command=led_toggle)
    btn_led.place(x=340, y=20, height=100, width=100)
    scale()
    
    
    def led_toggle():
        global led_status
        if led_status == "aus":
           GPIO.output(3,True)
           led_status = "an"
           btn_led.config(bg = "green",text = "Bewaesserung\n laeuft")
        else:
           GPIO.output(3,False)
           led_status = "aus"
           btn_led.config(bg = "red", text = "Bewaesserung\n kann\n gestartet\n werden")

    def scale():            #scale erstellen und wert auslesen
        def scale_value():
            wert = 0
            global scale_wert
            scale_wert = scale1.get()
            led_automatisch()
        global scale_vorhanden
        if scale_vorhanden == "nein":
            scale1 = Scale(led, from_=0, to=200, length = 200, orient=HORIZONTAL)
            scale1.place(x=340, y=20)
            scale_vorhanden = "ja"
            Button(led, text="Setzen", command=scale_value).place(x=340, y=50)

    
    
def led_automatisch():          #Scale Wert aus globaler variable einlesen, mit wert vergleichen und hochzaehlen
    global scale_wert
    wert = 0
    print(wert)
    while wert <= scale_wert:
       GPIO.output(3,True)
       wert = wert +1
       warten.after(1000,led_automatisch)
       print(wert)
    else:
       GPIO.output(3,False)


def main():         #starte hauptmenue und loop 
    hauptmenue()
    root.mainloop()

if __name__ == '__main__':
        main()