If the metric you're looking for is most accurate spectrum including deep red, near and far infrared (heat), then a good old incandescent filament light is the most efficient device. Not LEDs.
In the winter a couple incandescent lights per room is often enough to warm it up. I went out of my way this winter to "seal up" my house, and the equivalent of 2-3 bulbs per room is enough to keep them livable - with a sweater and a cap, and maybe socks. I cannot stand artificial heat, something about kt makes me physically uncomfortable, and i just want to leave an area with artificial heat. I'm fine with fires and incadescent bulbs, though.