In hindsight, perhaps I should have phrased it better. When I said "intensity", I meant it purely in terms of the photon density. I shouldn't have said intensity, because by definition it is the power per unit area. If we feed any two LED's the same power, regardless of their colour, the output intensities will be equal. (You get the same as what you put in). So, in terms of the actual definition of intensity, both LED's are the same as long as their input powers are the same.



However, in the same case, the red LED with the longer wavelength will light up brighter, because it has greater photon density than the blue one.



You can think of it as follows: There are two pools of same sizes, and they are both full. You empty one pool using 0.5L bottles, and the other one with 1L bottles. At the end, you will end up with more 0.5L bottles, (therefore a brighter LED) than the 1L bottles. But the total amount of water inside the bottles (energy/intensity) are equal. Hopefully this clarifies the ambiguity.