some observation and points on the thread.
#1) Crossroads , IMHO, is an expert on the shift registers, he has done many things with them and has the projects and has helped many-many on here figure out the problems.
and to answer your question. yes, you can daisy chain shift registers. of the TCIP595 Crossroads mentioned has 8 outputs. you can connect 8 of those chips and control them from a few pins (3 or 4 logic pins) from an Arduino. So, 8 chips for 64 outputs by using 3 logic pins is possible. other limitations apply, distance between chips for one.
#2) each house / building, etc, has multiple circuits. often one room might have 2 or even 3 circuits.
in another life, when upgrading a mains breaker panel, we would re-wire the circuits so the ones you would find nearest the bedroom doors were common as the vacuum was the most used device on that circuit. the ones by the beds were mostly used for alarms and heated blankets. In those days, you never wanted that circuit to trip. clocks had to be re-set.
The lights were on yet another circuit so when you did use too much power and tripped a breaker, you could see where you are.
For lighting like this, making multiple 'boxes' and plugging them into wall outlets that are fed by different breakers is a must.
You can easily find out by trying it, then, when the breaker trips, see what other outlets in the area are still hot. there is that separate circuit.
I think an Arduino current monitor might be a fun project.
#3) photography is an art. artists like to do things in a way that offers striking impacts. and there is a fade up and a fade down to incandescent lamps. Like tubes and music, they are more comfortable for humans. technically, there are other ways, but artists follow their own path and when done in some magical way, we get inspired and awe struck by the results.
#4) Zero-Crossing. we don't talk much about zero-crossing relays in the hobby world, but you can modify a relay to only change state at zero crossing. it does not impact the filiment as much and humans cannot detect the time difference. The ones I use for work are about $125 each for a specific lighting control panel.
the DMX, I think (do NOT assume I know ) has a delay from the control signal to the light going on.
...doing stage lighting in another life..... the lighting director had to flip the switch before the beat, you can tell a good director when the lights and the music were actually in time. Today, I think the computers allow for that and it becomes computer driven.
the old joke..... if you ever want to know who is the sound man in the band, just ask, 'who is the sound man' the guy that yells "WHAT?" well, that's him !#4) lots of people use relays and Christmas lights on their houses. the technology is comparable. but, you will burn out lamps more frequently. the OP did not say how long or how often the project is to be used. if for a 2 week photo shoot, all is great. if for a permanent display in a mall.... much needs to be discussed.
If you have ever seen a tail light of a car just go off, that was the early LED application. now they fade them off and on.
they mimic the incandescent lamp.
You can mimic an incandescent with a fade up and fade down. but not using relays. You would need to use something else.
not sure of your skills or your budget. you can get electrical switch boxes in metal that are gangable. they have removeable sides and can connect to make a long row. 8 in a row, with duplex receptacles (here in the USA) you can remove one tab on the side of the receptacle and turn them into 16 individually controlled outlets. leave the other tab for power. by using all store-bought parts, you are at least maintaining a basic level of compliance to codes.
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