The goal of this study is to find out the optimal luminance and color temperature of front light for reflective displays in
different ambient illumination by conducting series of psychophysical experiments. A color and brightness tunable front
light device with ten LED units was built and been calibrated to present 256 luminance levels and 13 different color
temperature at fixed luminance of 200 cd/m<sup>2</sup>. The experiment results revealed the best luminance and color temperature
settings for human observers under different ambient illuminant, which could also assist the e-paper manufacturers to
design front light device, and present the best image quality on reflective displays. Furthermore, a similar experiment
procedure was conducted by utilizing new flexible e-signage display developed by ITRI and an optimal front light device
for the new display panel has been designed and utilized.