One of important objectives on display market is to provide natural and realistic images. Specifications which are high dynamic range, high bit-depth, large gamut size, efficient data compression, etc. are demanded for achieving this objective. For high dynamic range (HDR), increase of maximum luminance is needed to present the brilliant sun realistically. Lower minimum luminance is better for complete darkness. As dynamic range is increased, dis-continuous perception of luminance difference between adjacent gray levels can be presented in display. Bit-depth is related to luminance difference between adjacent gray levels. Dis-continuous perception due to HDR can be reduced by high bit-depth. But, high bit-depth is caused of high cost for manufacturing display. Therefore, minimally required bit-depth should be determined for prohibiting contour. The objective of this paper is to present perceived bit-depth on display for TV with HDR. To achieve the objective, methods for visual test are proposed in this paper. As experimental results, bit-depth of 12 bit is enough to prohibit contour perceptually in OLED TV which has dynamic range over 100000 : 1.