For an analysis on the relationship between the photoelectric properties of a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) and the spectral characteristics of cold cathode fluorescent lamp (CCFL) backlight, a few spectrum filters were used in the electrical measurement of the photocurrents in a-Si:H TFT and the results were investigated and analyzed. When the backlights were transmitted through the various white spectrum filers and illuminated to the a-Si:H layers of TFT, the obtained photocurrents showed that the off state currents are related to the transmittance at the lower wavelength because the absorption coefficient of a-Si:H layer is reversely proportional to the wavelength of incident light and almost all the absorptions of light are carried out at lower wavelength than about 500 similar to 600 nm.