I do not have actual numbers on hand, but my understanding is that a dimmed incandescent bulb is even more energy inefficient compared to a dimmed LED or even CFL.

Incandescent bulbs have maximum efficiency (such as it is) at full voltage and brightness. As the power is dialed back, brightness and efficiency go down faster. 50% brightness uses much more than 50% energy for an incandescent bulb.

With LED Lamps I would expect the relationship between power consumed and brightness to be more linear as the lamp is dimmed.