Here's a simple PWM add-on :-
View attachment 141291
The output would connect to one of the inputs to IC1a in Sensacell's circuit.

Thank you Alec_t, I am getting some great and wonderful suggestions..
I never thought that my original post would result in so many replies and views!
Many thanks to everyone... ...don't stop, keep them coming!

 

Here's the revised circuit, as per my edit to post #80. Pot1 sets the dusk/dawn threshold and Pot2 sets the PWM duty cycle to vary the LED strip brightness.

R-LEDs is a current-limiting resistor, assumed integrated in the LED strip.
Any unused gates in the IC should have their inputs connected to ground or Vdd, so that they aren't left floating.

 

Here's the revised circuit, as per my edit to post #80. Pot1 sets the dusk/dawn threshold and Pot2 sets the PWM duty cycle to vary the LED strip brightness.
View attachment 141333
R-LEDs is a current-limiting resistor, assumed integrated in the LED strip.
Any unused gates in the IC should have their inputs connected to ground or Vdd, so that they aren't left floating.

Very nice!

Might ganging up the 3 remaining gates in parallel to drive the FET allow you enough drive to ditch the complimentary pair?
This trick should get you a driver impedance of around 160 ohms?

Probably should add a bypass cap to manage the gate current spikes too.

 

Here's the revised circuit, as per my edit to post #80. Pot1 sets the dusk/dawn threshold and Pot2 sets the PWM duty cycle to vary the LED strip brightness.
View attachment 141333
R-LEDs is a current-limiting resistor, assumed integrated in the LED strip.
Any unused gates in the IC should have their inputs connected to ground or Vdd, so that they aren't left floating.

Thank you Alec_t - this is actually very good - I like it!
At first I thought Pot1 and the LDR were reversed but it appears ok
Are the transistors and R2 needed or can IC1b be connected directly into the MOSFET?
Edit: Sensacell replied as I was writing this

 

Referring to Sensacell's post #71 and also my post #74

I was actually doing some calculations last night and it seems that I would need about a 15k resistor (R1)
to fix the threshold of when the light comes on.
Referring to the 4093 datasheet and due to the hysteresis of the 4093, the circuit activates (light comes on) when the LDR is about 70k and deactivates (light switches off) when the LDR is about 40k - which is what I wanted.

 

can IC1b be connected directly into the MOSFET?

The 4093 is rated for low output current only. You could try without the transistors, but I'd retain R2 and increase its value to, say, ~1k to reduce stress on the IC1b output. You could also connect currently unused IC1c and IC1d in parallel with IC1b so that three Schmitt gates share the load of driving the M1 gate capacitance.

Edit: And as Sensacell suggests, the IC would benefit from a decoupled supply. A short-leaded 100nF ceramic cap between pins 7 and 14 may be enough.

 

You could also connect currently unused IC1c and IC1d in parallel with IC1b so that three Schmitt gates share the load of driving the M1 gate capacitance.
.

Thanks again Alec_t, I like this idea, it will make PCB routing very easy.