outsider:
Do you really need to know the voltage? 1.5 V = ADC value of 307 (with 5V AREF):if((analogRead(IRS)>=307) && (digitalRead(ILSH)==1)
I just had a curve (maybe not the good word, sorry for the English ^^") showing how much volts I get for how much centimeters of detection, the 1.5V are just between 5 and 17cm in that case