2. How efficient is the LED light source?

Efficacy is the specification that measures the efficiency of a light source by comparing lumen output to wattage consumed.
Efficacy is derived by dividing wattage consumed into lumens emitted.

The higher the efficacy number, the more efficient the fixture.

All published specifications for WAC Lighting LED fixtures are based on testing complete fixtures.

It's always good to verify that the published data from the manufacturer is tested for input wattage and total lumens as a complete fixture. If the specifications are only for the LEDs as tested in laboratory conditions, the true performance of the fixture may be less.