We have developed an advanced computational model for predicting the brightness achieved by HDR (high dynamic range) televisions and computer monitors, in particular those with materials that feature primary colors having high spectral purity. The technological integration of quantum dot materials and emissive pixel lighting is expanding the color gamut level to attain a degree of performance unmatched in today’s consumer and professional displays. In fact, the migration toward 8K ultra-high definition (UHD) products, in most cases, is being closely coupled with displays that use a wide gamut for elevated performance. These displays exhibit highly significant improvements in saturation and brightness due to the H-K (Helmholtz-Kohlrausch) effect, where people perceive some colors—notably reds and blues―as far brighter than any current model would predict. Our experiments thoroughly tested a new model and compared subjective findings from television sets with high luminance and a very wide color gamut, which were ideal for re-assessing the H-K effect. We achieved a suitable model and quantitative metric by blending the iCAM06 computational model originally designed for HDR image evaluation with a much improved treatment of vivid colors. Our data methodology relies on a one-of-a-kind 2D spectroradiometer that captures up to 1.4 million samples of spectral data across any image, an achievement impossible to attain manually. Our approach coupled nicely with the filter image-processing steps in iCAM06. Finally, we extracted image brightness for determining the SEMI Perceptual Contrast Length (PCL) improvement level of our model, then matched those results to subjective experiments. As a result, we have a high-accuracy model that can be used by display makers to predict set brightness as a function of color saturation and optimize luminance—notably for reducing power—in displays with spectrally pure primaries.