Another variable, luminance ratio (LR)--the ratio of average luminance to window luminance, is defined and considered as an indicator of the brightness contrast between daylight source and the whole visual field.
Models with four types of variable combinations based on three variables are developed and compared --model with only vertical illuminance (Ev model), model with vertical illuminance and shade position (Ev+SP model), model with luminance ratio and shade position (Lr+SP model) as well as model with three variables (Ev+Lr+SP model).
The process covers two ranges of tests: optical performance, which includes testing for luminance ratio
, color, uniformity; and physical performance, to check correct functioning after exposure to water/dust ingress, vibration, impact, and temperature cycling.
Conclusions from previous studies [Osterhaus 2002, NUTEK 1994] were a reference to set the lower level of L below 1.5 x [10.sup.3] cd/[m.sup.2] and a luminance ratio
between task and window below 1:100, and the higher level above 1.5 x [10.sup.3] cd/[m.sup.2] with a luminance ratio
[C.sub.R] is ratio of the highest and lowest luminance values and is used to describe features of electronic devices, mostly dispalys .
Bezold-Brucke hue-shift as functions of luminance level, luminance ratio
, interstimulus interval and adapting white for aperture and object colors.
This conclusion implies that perceived contrast for light-on-dark symbology is determined entirely by contrast ratio (i.e., the luminance ratio
between the background and the most luminous pixels constituting the symbol) and is not affected by antialiasing.
Existing guidelines (for example, the ILE Outdoor Lighting Guide [ILE 2005]) tend to recommend a luminance ratio
between an object and its background according to the degree of conspicuity (saliency) required, with a higher luminance contrast being recommended for a higher degree of conspicuity.
* Productivity can be diminished when glare, ceiling reflections, visual comfort probability, luminance ratios
, spacing criteria (SC), and flicker effects are not considered.
The IESNA has developed guidelines for acceptable levels of nonuniformity expressed in terms of luminance ratios
between surfaces in the FOV.
IBL technique is particularly useful for visual comfort and performance metrics, where interior luminance ratios
and accurate depiction of window luminance distributions are critical.