So far we have covered the basic ideas of voltage, current, and resistance. This is good for lighting up LEDs, but for doing work in the real world, what is really needed is power. This chapter on its own adds very little to your capabilities as a circuit designer, but it is absolutely critical background information for the chapters that follow. Additionally, this chapter contains information critical to the safe usage of electronics. Knowing about power, power conversions, and power dissipation will be critical to taking your electronics abilities into the real world.
It is actually much less than 11 W, since LEDs are not perfectly efficient either. The point is that since they are both emitting the same amount of light (i.e., producing the same light energy), we can see that the difference in watts used is probably lost in heat.
As a sidenote, if you tried to wire a regular AC transformer to a DC power supply, it would not deliver any power at all—DC-DC converters work on very different principles than AC transformers.
