Hi everyone. To begin I will write out a quick description of what I am trying to accomplish. I'm in the process of building and completing a Split Hopkinson (Kolsky) Bar. I'm in the works of creating a device that will read the speed of my striker bar as it passes through the gas gun. Is there anyway to hook up two separate LED's to a single Arduino, point two separate lasers into the LED's then hook the Arduino to an oscilloscope to measure the breaks of light in the LED? In other words "use the breaks in the laser to determine the speed of the striker bar passing through the two separate trip wires".
LEDs can be used as light detectors, but it would be more usual to use normal photodiodes.
Do you have a reason to use LEDs?
What is the smallest time frame you need to detect and to what accuracy?
LEDs can actually be just as efficient as photodiodes, especially at high speeds. But no other reason than that. I'm shooting a striker bar around at most 150fps or 40m/s over a 3 foot bar length. So we will be in the microseconds to obtain an accurate velocity profile.
They use lasers in movies because it looks cool. Real beam-break detectors use regular light. Usually infrared so the source is invisible but it is still not a laser.
You don't even need especially fast sensors either. If the analog output reaches the low-light threshold hundreds of nanoseconds 'late' then it will be the same for both sensors and the speed calculation is unaffected.
Keep googling. This is a pretty common type of thing that the Arduino is good at.