[wlesieutre]

Only if you have resistive electric heat. Resistive heat is a simple X electricity -> X heat added to house. A heat pump uses electricity to move heat from one object to another, so it's X electricity -> Y heat pumped into the house from outside, where Y has some efficiency limits, but isn't directly bound by conservation of energy.

The effective heat gain here is more than 100% of the electricity spent, and we measure it with "Coefficient of Performance" instead of "efficiency". A good system is somewhere around CoP 3.5, making the LEDs a comparatively bad heater.

[goda90]

I don't think his point is that it's a great source of heat, just that electricity used on the LEDs is either being used as light by the plants, or as heat by the occupants of the house, so in a sense, the waste is minimal