Short pulses through some 5mm LEDs.
The Top Trace is always the detected light.
RED Led 1us ~80mA pulses, - from long ago.
Green Led 0.5us ~110mA,
Super bright Med White Led 0.5us ~30mA, ~300X more light per mA than the standard green LED.
1us, Red, Green, White, 5mm.
I don't know why Red LEDs usually give a more curved top light shape, I don't think it can be a photodiode thing because the top of the current shape through the LED matches it, - curved for red and flat for green.