Chrony readings LED lighting vs Natural lights

I use a pair of LED pucks on top of the diffusers. I use it frequently at night and it gives readings that are consistent with those during the day. The chronograph is a Competition Electronics Prochrono but I don’t have any reason to think a different chronograph would work differently.

It is true that a single light source placed so near the chronograph will give elevated velocities because the projectile’s shadow will reach the two sensors closer in time.

Maybe try the lights on top of the diffusers?

Another possibility to consider is whether the LEDs are steady state (constant current) or flashing at high speed (pulse-width modulation). Some LEDs are actually flashed at a very high speed, and the brightness is controlled by the ratio of time on versus time off for each pulse. Longer "on" times mean brighter light. These high frequency pulses are faster than your eye can detect, but can create a strobe effect that throws your chrony readings off. Don't worry, there's a simple test to tell the difference. Shine your LED lights on a small fan while it is running at high speed. A ceiling fan turns too slow, but a small box fan usually works well. If your LED makes the fan look like a blurry disk, then it is steady state. If you see the fan blades appear to be moving much slower than they really are, then your LED is flashing like a high-speed strobe light, and may be the reason for your strange readings. I use a pocket LED flashlight that uses a single AA battery. When I look at cooler and freezer fans with it at work, I get the strobe effect because it is a pulse-width modulated LED. Hope this helps identify or eliminate the LEDs as the source of your issue.

I use the manufacturer's LED red light kit (about $70) and have had absolutely zero issues with the readings being different between the artificial light and daylight.