6500K is no reduction. 1900K is the maximum reduction using the default settings. You can go as warm as 1200K with the slider if you enable the setting to enable the wider slider ranges, and you can go as warm as 800K if you use the keyboard shortcut Shift+Alt+Page Down. The lower the Kelvin value (K), the less blue light there is. 800K is pretty much just red.
However, due to varying differences between the color accuracy of monitors, no two can be identical. So, 1900K on your monitor likely has a different appearance than it does on mine or anyone's monitor.
Just use a setting that enables you to relax and feel comfortable and sleepy at night during the last hour or two or three before bed at the end of your day. Combine a warm color temperature setting with a lower monitor brightness (you'll have to do it separately using the buttons on your monitor or laptop keyboard).