Current Sensor ACS712 not changing its value even when connected bulb is lit
In a comment about rZero = 511;, you wrote:

For illustrative purposes only - should be measured to calibrate
sensor.

This may well be the cause of your problem. If, instead of 511, the
“zero” of your measurement is around 445, then you end up measuring a
non-existing DC current of about 3.23 A. When you turn on the light
bulb, you add roughly 435 mA (100 W / 230 V) of AC
current. The total RMS current you see is then:
√(3.232 + 0.4352) ≈ 3.26 A
Barely visible at the resolution at which you are printing the result.
And this is assuming you are using a 100 W bulb, as shown in the
diagram. These bulbs are getting hard to come by. If you are using
anything less powerful, you may not see any change in the displayed
value.
As a quick and dirty fix, you may replace 511 by 445. A better
solution would be to compute the quadratic average of the AC part of the
signal alone. In other words, compute:
√(average(current2) − average(current)2)