Appearance in High Dynamic Range (HDR) images is controlled by intraocular glare and simultaneous contrast. This paper describes unique test targets that simulate real images. They change the HDR range by 500 times without significantly changing the veiling glare on the retina. As well, these targets have nearly constant simultaneous contrast. Using these test targets we measured the range of appearances possible from HDR images with different average luminances. The targets displayed a maximum luminance range of 5.4 log unit. Hoverever, the results show that the usable range of luminances for a full range of appearances (white to black) is much smaller.