Please see the question and answers below: A source of red light has the same wa

Question

Please see the question and answers below:

A source of red light has the same wattage (i.e. same power output) as a source of green light. Which of the following statements are true about these two light sources?
True: the green lamp emits higher-energy photons than the red lamp
False: the green lamp emits the same number of photons per second as the red lamp
True: the two lamps emit the same amount of total energy per second
True: the red lamp emits photons of a longer wavelength than the green lamp
False: the green lamp emits more photons per second than the red lamp

Why do the two lamps emit the same amount of total energy per second? I thought the green lamp would emit more total energy per second because the frequency of green light is higher than the frequency of red light. And shouldn't the green lamp emit the same amount of photons per second as the red lamp since the power is the same? I thought that power and intensity were directly proportional, the intensity of the light would be the same for both.

Could someone explain this to me better?

Thank you

Explanation / Answer

The lights emit the same amount of energy per second because that is in the problem statement: they have the same wattage (power output). It's a given. Power is energy per second, one watt is one joule per second. The green lamp emits fewer photons because a green photon has more energy than a red photon. The intensity of the light should be the same for both, because the power is identical, that is true; but the smaller number of green photons carries as much energy as the larger number of red photons.

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