The ColorMunki software includes a control to measure the ambient light in your viewing area and adjust your monitor's brightness to match. However, depending on the amount of control you have over your ambient light conditions you may get a result that is more dark than expected. In this case, you may find that you have far better results by using the industry-standard of 120cd/m2.

That said, the ColorMunki software has a threshold that needs to read somewhere around 350-400 LUX to get a target luminance above the 80 threshold.