Hi @chengjh1, we are indeed constantly working on improving our products and with upcoming eye trackers we are reducing considerably any visible light for users however the hardware for the 4C is fixed so I am afraid we are quite limited in the ability to reduce this effect.
The 4C does indeed operate on infrared light but the illuminators are such that some light does enter into the red part of the spectrum.
Apologies for the inconvenience, we hope this will not unduly effect your study.