Yes,measuring the energy consumption and efficiency of the conversion from electricity to light is part of the label. The light bulb example is not as unsuitable as you seem to assume. Incandescent light bulbs only convert about 5 percent of the energy consumed to light, the rest is converted to heat. LEDs, in contrast, are 6 to 8 times more efficient.

Your "does image processing..." part is also important. Different processors consume vastly different amounts of energy. A hobbyist example would be trying to run something on a battery powered ESP32 with or without deep sleep.