Calculations appear in a second browser window after clicking "Calculate".   You may switch back and forth between these windows, revisit this page, load different IES files and change settings as required.  Resultant wattage and quantity may be input to an ROI payback calculator.

The preset values evolved from RP-20 and can be adjusted to suit requirements. 

Minimum Illuminance  sets the threshold values for the conforming (green) and non-conforming (red) display.  An outdoor parking lot has values different than an indoor parking garage, thus each has a Horizontal and Vertical min. illuminance value.  Horizontal illuminance = footcandles measured level at the floor, vertical illuminance = footcandles measured 60-inches above with light meter perpendicular to the floor.  Note that vertical illuminance should be 1/2 the value of horizontal illuminance at the lowest unshadowed point between luminaires.

Horiz. Uniformity  for horizontal illuminance is the ratio of Maximum footcandles divided by the Minimum footcandles in the lighted area.  Note that Max/Min rather than Avg/Min is used for parking facilities.  See Min. Uniformity Multiplier below for options.

Cutoff  applies only to outdoor parking lots, and defines the output limits from 80° to 90° and, 90° and higher.  See Cutoff Defined.

Min. Uniformity Factor  Since the area defined by the table will usually exceed the lighted area, a minimum setting multiplier is provided to define that outer limit.  This multiplier limits the lowest value that will be used in the Uniformity Ratio calculation, e.g. a multiplier of 0.1 limits the minimum for an outdoor parking lot to 0.02 footcandles, or 0.1 footcandles for a parking garage.  The designer must provide a lighting layout with sufficient overlap to bring this boundary up to minimum illuminance levels.

Mounting Height  This value is used to calculate all angles for illuminance.  A 14-ft Mounting Height distinguishes between parking lot or parking garage. Limit is 8 to 40 feet.

Candela Multiplier factors all candela in the IES file to scale up or down.   Used when a single file is supplied for a family of luminaires, needing only a multiplier above or below the base lumens, usually provided.  Wattage and relative lumens display are changed accordingly.

Rotate Luminaire  allows rearranging lighting peaks or lobes to other horizontal positions.  Note the display has different band widths: the 90° and 270° bands are centered within a 45° swath, while the 0° and 180° are centered within 90°.  Rotate can allow a finer resolution with a Type-I distribution, for example, but has little or no effect with symmetrical outputs such as type-5.

Show Candela / File Headers  are display options having no effect on analysis.