Fluorescence images of HeLa cells expressing EGFP, EYFP, or mKate2. The luciferin concentration in the culture medium ranged from 0 to 2 mM. A: EGFP images captured by filter set 1, 2, or 3. EM‐CCD gain, 410; exposure time, 150 ms. B: EYFP images captured with filter set 1, 2, or 3. EM‐CCD gain, 208; exposure time, 150 ms. C: mKate2 images captured with filter set 4. EM‐CCD gain, 700; exposure time; 150 ms. All images are shown with no level adjustment. Filter set 1, BP460‐480HQ (Ex) and FF01 550/49‐25 (Em); set 2, BP490‐500YFP (Ex) and FF01 550/49‐25 (Em); set 3, FF01 500/10‐25 (Ex) and FF01 550/49‐25 (Em); set 4, BP545‐580 (Ex) and 610ALP (Em). Ex, excitation; Em, emission; Scale bar, 20 μm.