Alexa enabled light bulbs

[Doctor_Wibble]

On a light switch you will usually have a single 'Live' loop (from the main lighting circuit) going through it with the switchy bit itself controlling whether the loop is complete to let the currants through or has a gap they can't cross. So although there is an in and an out, the in is Live (L1) but the out (L2) is not Neutral, it is also Live but not always live.
The light fitting with the bulb in it will have Live currants (coming in from the switch) and Neutral going out to join the main lighting circuit.
So there is a Neutral but not in that particular part of the ensemble, it is for the 'used' currants after they are burnt in the bulb to make light .
Live --> switch --> bulb --> Neutral.

As noted above, exact details will vary depending on whether it is a single switch, a paired switch (like top/bottom of stairs), off to the side of the wires going to the light, or on the way...

Oblig. Disclaimer E&OE
Especially if my umpteen rewrites mangled the logic and made it all the wrong way round
Neutral can zap you just like Live does.
Always be careful when deciding something must surely be 'neutral', remember that this does not mean no voltage on it, switch off the circuit before opening anything, and use a voltmeter or a volt-detector anyway but check those work before trusting your life to them

If in doubt, get it done by a mate who says he did a bit of that wiring malarkey once.

[Astra LeMort]

Well explained Doc. I must admit, I'd forgotten that the neutral in a standard lighting circuit is not really neutral (I vaguely remember reading about it once!). Whenever I've replaced a light fitting or switch, I've simply wired it exactly the same as the one I've removed, without really thinking about what each individual wire does.

I've managed not to electrocute myself so far

[Doctor_Wibble]

... Whenever I've replaced a light fitting or switch, I've simply wired it exactly the same as the one I've removed,...

And absolutely in line with the requirements of "if it ain't broke", a central tenet of the principles of Part P as regards whether or not an officially qualified person is supposed to be wielding the screwdriver, addendum to which 'if I do this carefully and neatly, nobody will see the need to ask'.