Contrast is a very important factor for designing to improve visibility, especially for older adults and low vision. An experimental study was conducted to clarify how much luminance contrast is necessary in visual signs for older people and people with low vision, using displayed patters of a simple border, squares and stripes consisting of square wave patterns. A total of 80 people including older people, people with low vision and younger people without any impairments as comparison, were participated in the experiment. Older people and people with low vision needed higher contrast than youngers did in general. In particular some patterns with high spatial frequencies were found more difficult to see for the older people and people with low vision than for youngers. It was also found that people with low vision were sometimes prefer to see in negative contrast than in positive contrast. The results of this study can be used for designing of built and outside environments to increase visibility of older people and low vision.