For the lighting in my apartment, I'm using a 12 volt power supply, as that's what the LED strips are fed because they put 3 in series times 3.6 volt drop or 11 volts plus a 220 ohm resistor. That's fairly efficient.
The problem is the Arduino or ESP board uses 5 volt or 3.3 volt power, and to get that right now I'm using a linear regulator, which "discards" the excess voltage as heat -- a device that draws 75 mA @ 3.3 VDC or a 0.24 watt, ends up drawing 75mA @ 12 VDC or 0.9 watts, with the linear discarding 0.66 watts as heat -- even when things are idling and doing no useful work.
Now, throwing 0.66 watts into a head won't exactly heat a room up, but that still a waste of 5.7 kW/h a year. But until now I hadn't found a small, inexpensive switching regulator for 55 cents a piece, which will cut into a lot of waste, although switch mode regulators still have some waste.