Figure 4. Dihydroethidium labeling of RGC-5 cells. Dihydroethidium labeling of RGC-5 cells showed that only filtered light (1000 lux; C) and not serum deprivation (B) caused the detectable production of reactive oxygen species (red fluorescence, as marked by the arrows), as compared with control cells incubated in the dark in the presence of 10% (v/v) serum (A), after 48 h. This effect did not appear to be obviously enhanced for cells incubated in serum free medium and exposed to light (D). The scale bar represents a distance of 20 μm.