The word down lights with encompass a whole range of lamps from MR11 equivalent to lamps with 12 inches across the lamp. Size does matter, take a MR16 spot and place a circle of frosted glass in front of it to defuse the light and it can transform what looks like a planetarium to a good even light. The problem with the MR16 equivalent LED lamp is they are often no 16/8 inch across the light source but much less where cooling fins take up a big chunk of the area. However the surface mount LED lamps have a larger surface area and include a defuser so will light the room rather well.
How one defuses the light does not really matter, be it an up lighter shining at the ceiling or a spot light shining at a white wall it will have the same result and the light is spread, this does not happen with a spot light shinning onto a darkish floor.
Without details of lamp being used, it is impossible to work out the spread. With a MR16 equivalent lamp they are not really equivalent, they don't have a multi-fasted reflector and they are not 2" (18/8") across. With any spot lamp one can look at the angle and use maths, but with the LED equivalent the cut off is not as great so we get for example a 25~35 when most of the light is at 25° but still gives out some light to 35° I use one in my bedroom and the beam is tight enough not to keep my wife awake when I am reading. But it is that tight mounted in the ceiling pointed down I would need one every 0.5 meters to light the room. To me unless a spot is aimed at a white surface to reflect the light it is useless to light a room.
I have a 11W I think 12" down lighter which I mounted in the corner of a set of wall cupboards in the other bedroom as a reading lamp it was given to me it was a 2D unit, now these are used a lot in public buildings and they do work, often mounted in ceiling tiles, however the square lighting panels which replace a ceiling tile in a suspended ceiling do work better.
Today with surface LED lights looking hardly any different to lamps requiring large holes being drilled and special hoods to retain the fire rating of the plaster board I just can't see the point in the old fashion 80's type MR16 lamp.
