BenQ TK850i has a rated brightness of 3,000 lumens. As we normally do here at Projector Reviews, I took 3-4 readings about 15-20% out from the center of the lens, which usually gives a pretty good approximation of ANSI lumens. At full wide angle, I measured the TK850i in its brightest picture mode, BRIGHT, with the lamp power set to NORMAL.
BenQ TK850i Brightness:  Lumens
At wide zoom, BRIGHT mode, the TK850i measured 3030 lumens. The TK850i was a little above its rated brightness, so it should be more than bright enough for most intended applications. I measured all five available brightness modes at wide-zoom, and my measurements are below.
The BenQ TK850i claims 3000 lumens. It was 3030 lumens measured in Bright mode (which is its brightest mode) with the zoom set to wide for maximum brightness, which is just a bit higher than their published ANSI Lumens specification.
ZOOM LENS POSITION'S EFFECT ON BRIGHTNESS
MEASURED BRIGHTNESS AT TELE-ZOOM
Bright Mode: 2880 Lumens
Our measurements found a roughly 38% drop going from full power (labeled Normal), down to Eco mode. Many projectors drop 25% to 35% when switching into their “eco” mode.
The TK850i has a third mode, Smart-Eco, which is a dynamic mode. As such, it will measure nearer Normal mode, when we feed it white for measurement. The TK850i uses TI’s Dynamic Black, which is definitely a plus. However, lamp dimming is always very minor, because lamps dim and brighten too slowly to get much “dynamic” range out of them without visible pumping. Visible pumping is a phenomenon in which the image lightens and darkens a bit at times when it should not.