This is due to the ambient room light. To become visible the projected image must have sufficient light to exceed the background light. Thus each installation has to deal with the particular conditions that exist for that screen and the normal light. In general the more lumens produced by the projector the brighter the screen image appears. Knowing the amount of lumens available from a projector permits predicting the image visibility and best size.
Native resolution is the normal resolution of the CRT monitor or laptop LCD screen.
LCD screens their inherent resolution is defined by the number of pixels making up the screen. You may want to think ahead about what your next computer will be and will the planned projector handle your new computer s display resolution. Projectors today will handle their native resolution and usually also compress the next higher level resolution. Compression uses a software program to determine the best way to display a higher resolution. Today s compression methods are so effective that it is difficult to tell the image has been compressed.