Hi @gendor,
I’m pretty sure we used these: Super Bright White 5mm LED (25 pack) : ID 754 : Adafruit Industries, Unique & fun DIY electronics and kits
However, we had a similar problem where were overexposing our (dilute) cultures to light, and only saw growth when we brought the LED intensity down to ~5% or something (and brought it up from there). I think we also used a higher RPM than we initially expected, like 500.