How to find if AC Appliance is on or off using ACS712 current Sensor
The code looks like it would produce rather larger values than you are seeing, if it gets correct inputs from the sensor.  For that reason, you probably should carefully check your wiring.  Also, with a DVM, measure the sensor output voltage with the light on and with it off, to verify sensor operation.  If you measure ok sensor voltages but don't get good readings, your analog input pin may have a problem; you could try other analog input pins.

Note, when debugging an issue like this, it does not make sense to run a few numbers through five levels of processing before printing anything out.  You should at least add serial prints in getVPP(), and just before returning the result, print out result, maxValue, and minValue.

Note, fix the erroneous comment “//root 2 is 0.707”; the square root of 2 is about 1.414213562, while 1/√2 = (√2)/2 is about 0.707106781.