Understanding Projection Terms

Distance from projector to screen:

Known as “throw distance”, this is the actual measurement from the front edge of a projector lens to the projection screen surface . While it may be expressed in feet, it should be converted to inches for practical use .

Farthest viewing distance:

The actual measured distance between the center of the displayed image and the farthest possible viewer’s eye location .

Foot-Lamberts(fL):

A foot-lambert equals 1/π or 0.3183 candela per square foot, or 3.426 candela per square meter .

LUX: Equal to one lumen per square meter

Light level:

The actual amount of light present in a room. Best measured by a light meter, it is expressed in LUX which is equal to 1 lumen per square meter .

LUX:

Equal to one lumen per square meter . In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface .

Image size:

The actual size of the display, typically expressed as the diagonal length, cornerto-corner .

Lens ratio:

The width of the image (W) relative to the throw distance (D) is known as the throw ratio (D/W) . The most common projector throw ratio is 2 .0 . This means that for each foot of image width, the projector needs to be 2 feet away or D/W = 2/1 = 2 .0 .

Video format:

The ratio between width and height of the displayed image . Expressed as a fraction with the lowest common denominator . (16:9 or 4:3)

Zoom range:

The zoom range is the difference in magnification from one end of the zoom range to the other . Expressed as the lens ratio at shortest and longest extents of the zoom range . (1 .39—2 .09:1)