No, because rectifiers are cheap commodity items, and you can wire all the LED lights in a house on a single 15A circuit and #14 wire (~1400 watts). You can also put ~140 32w 2’x4’ LED fixtures on a 277v 20A circuit using #12 wire. It’s cheaper and easier to convert at the fixture or lamp and just use standard wire for everything.
If there was anything to be gained from doing it that way, it would already be done in commercial build outs.
Low voltage requires low resistance to transmit reasonable current. The only way to get this is with substantially thicker wiring.
5V DC isn't a plausible voltage to send the distance from a fusebox to light installations. One could do 48V and step it down at the site, but there's not much in the way of gains to be had. AC/DC circuits are quite efficient as-is.
> PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA[2][3]) on each port.[4] Only 12.95 W is assured to be available at the powered device as some power dissipates in the cable.
84% efficiency sucks. It's a reasonable solution for some cases, because if you're running Ethernet to a camera already, hey, why not provide some power?
But for, let's say 300W of lighting that runs 12 hours a day, you're wasting about 15kWh of electricity per month. Residential wiring has internal losses under 1%.
PoE is popular because electricians are expensive. That said I think there is a lot of potential to use the newer higher power PoE standards or similar for smart houses. The newer standard go up to 100W.
One thing about efficiency is low voltage DC/DC converters are always fighting for efficiency. It's much less of a problem for higher voltage DC/DC's. This is due to fixed voltage drops and I squared R losses.
