This paper presents results of perceptible and acceptable ranges for color gamut change of transparent liquid crystal display (LCD) by luminous sources. Color gamut of transparent LCD can be changed by external luminous source because LCD cannot emit by itself. In this paper, perceptible and acceptable ranges to optimize color gamut for transparent LCD were found by psychophysical experiments. External luminous sources which have color temperatures of 3000, 5000 and 6500K were used. As a result, the differences of perceptible and acceptable ranges of color gamut using light sources are about 3% and 18% respectively. In addition, the differences of perceptible and acceptable range were investigated according to illuminance of external luminous. The difference of perceptible ranges does not affect the illuminance intensity. When the intensity of illuminance was high, the acceptable range was decreased than low illuminance. When the color gamut of transparent LCD has decreased within acceptable ranges, most observers can permit the image quality regardless of light source. In other words, transparent LCD which has somewhat narrow color gamut can be permitted.