two rays of different wavelength will generate the same electric current ?

Photodiodes have rather uneven frequency responses, mainly dependent on the material they're made of . google on "photodiode datasheet", they often show the curves. IIRC silicon peaks in the infrared, with a long tail into the visible. Many have special filters right on the chip, to modify the response. for a real treat, go to

Typically no, the difference won't be enough to determine which one is shining.

Aiming the optics correctly will in most cases make a greater difference than the wavelength of the illumination.

If you're wanting to detect colours consider putting filters in front of the photodiodes to block the unwanted wavelengths. (have one to detect red and one to detct green) or using coded signals from the LEDs (this will increase the operating range of the system over just running the LED as a constant brightness - eg use 40Khz for one led and 30Khz for the other)

Bye. Jasen

In the case of semiconductor diodes, the current is unlikely to be the same, because different colors are not absorbed equally efficiently. Except for the efficiency issue, the current could be the same when the diode is operated into a short circuit, but would be different if the photodiode was allowed to run at higher output voltages, i.e. the output power-delivered-into-a-load would be color dependent even if current into a short circuit (which is a no-load condition) was the same.

In the old sense, a photoelectric cell (vacuum tube) is a kind of photodiode, and those have VERY STRONG dependence on the color. The metal of the cathode (the photosensing metal plate in the tube) can be completely insensitive to colors which are redder than necessary to overcome the electronic attraction to the metal (the 'work function' of the metal). This photoelectric effect was a strong clue to the developers of quantum mechanics, and successful explanation of the effect earned young Albert Einstein a Nobel prize.