The Apple TV set-top box (STB), which I own, has always been very energy efficient. It is consistently at top the of EPA's ENERGY STAR STB ratings.

The newest Apple TV, the "4K" model, is not yet in the ENERGY STAR database, so we don't know if new features affected the box's power consumption. Apple does prove the following information in its tech specs:

Apple TV 4K
BFR-free & PVC-free
Meets ENERGY STAR 5.0 requirements
Siri Remote
Arsenic-free glass
BFR-free & PVC-free
Recyclable aluminum enclosure

2013

AnandTech tested the Apple TV A1469 model in 2013 and reports, "The power savings are nothing short of significant. The previous generation Apple TV wasn’t really a power hog, with platform power maxing out at around 1.6W, but the new model tops out at just a watt. Overall the power savings seem to be around 800mW across the board."

Reviewer Anand Lal Shimpi goes on to speculate about the future role of the box's A5 processor: "With no change to process [sic] technology, I can only assume that the reduction in power consumption came from other architectural or silicon optimizations. The significant power reduction is the only thing that makes me wonder if this new A5 silicon isn’t destined for another device, perhaps one powered by a battery. That’s pure speculation however, it could very well be that the A5 in the Apple TV is just lower power for the sake of being better designed."

Apple says, "Apple TV is designed with the following features to reduce its environmental impact:
Brominated flame retardant-free
PVC-free
Meets ENERGY STAR 3.0 requirements for set-top boxes"

More about Apple and Green ICT.

More about STBs and Green ICT

Image courtesy Apple