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If they are so inefficient then where does the wasted energy go?

Where it always goes, waste heat. In the case of LEDs, about 50% to 60% of the power draw escapes as heat. Of course, incandescents are much worse.

70% near heat would the very very efficient blue leds, properly driven and all. below that, i.e. 50-60 is just theoretically impossible.

The wasted energy as per usual - heat/entropy. It's just that LEDs are the best we have.