An LED specification system is provided having at least one LED light output device. The LED light output device has an LED light source, a first exchangeable face panel selectable from a plurality of potential exchangeable face panels, and a housing for locating the exchangeable face panel relative to the LED light source and for orienting the LED light source such that light from the LED light source passes through the first exchangeable face panel. The LED specification system further includes a user interface for selecting at least one preferred output characteristic for light from the LED light output device. The preferred output characteristic is defined by a metric value. The LED specification system further includes a transformation module for defining an LED specification value based at least partially on the defined metric value and a characteristic of the LED light source.