You can't have a low-voltage DC power supply supplying the entire home: the voltage drop between the supply and the LED would be huge. There's a reason we use

You can't have a low-voltage DC power supply supplying the entire home: the voltage drop between the supply and the LED would be huge. There's a reason we use higher voltages for long wire lengths: to increase efficiency and reduce line losses, since losses increase geometrically with the square of the current (according to Ohm's Law: P = R * I^2). Higher voltage means proportionally lower current, and geometrically lower losses. And since we need high voltage (at least 100V) to keep line losses very low and allow the use of thinner-gauge copper wiring, we need a switching power supply at every light fixture, so it really doesn't matter if it's AC or DC, since modern SMPS (switch-mode power supplies) work equally well with either. Finally, on top of all that, LEDs are current-driven devices, and need a constant-current power supply. So the power supply must be very close to the diodes, or else fluctuations in supply voltage will have very negative effects.