Measured the light bar on each different setting. I used a colorimeter and a spectrometer which are typically used for color calibration on displays, but they also measure luminance/light. They're probably not 100% accurate compared to a dedicated light meter, but they should be close enough. I averaged the readings with a continuous measurement between both meters.
Standard/Bright - ~37.9 candelas per squared meter (or 11.06 foot lamberts)
Medium - ~21.8 candelas per squared meter (or 6.36 foot lamberts) - 42.5% dimmer
Dim - ~11.8 candelas per squared meter (or 3.44 foot lamberts) - 68.9% dimmer
So my guesses of ~60% and ~40% lower were pretty close.
For comparison, generally ISF/THX calibrators calibrate flatpanel displays to have a peak white measurement of 30-35 foot lamberts for a dark home theater environment. VA LCD panels usually have a black level measurement between 0.012 - 0.014 foot lamberts. IPS LCD panels usually have a black level measurement between 0.04 - 0.05 foot lamberts.
