demonstrated that patients achieved better VA when using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart, which has a background luminance
of 121.0 cd/[m.sup.2], than when using the standard Snellen chart, which has a background luminance
of 65.0 cd/[m.sup.2].
In the dark region, [alpha] = 0, indicating that the perceived contrast doesn't depend on the background luminance
and is a function only of the absolute luminance difference [DELTA]B.
Stimuli are presented upon a liquid crystal display screen, at a mesopic background luminance
• RVR Measurement System based on forward-scatter meters equipped with background luminance
(ambient light) sensor.
As Weber's Law  says, the just noticeable difference in terms of luminance between two regions is approximately proportional to the background luminance
. The ringing map r(x, y) can be regarded as the luminance difference caused by ringing structures.
The notion that, in older adults, contrast sensitivity impairment increases with decreasing background luminance
and that the determinants of this phenomenon are partially neural is not new in the literature (10,26).
Target and background luminance
levels (Lt and [L.sub.b]) were measured by luminance meter.
As it was already mentioned that the size, background luminance
, and luminance contrast of the visual target determines its visibility, the age of the observer should be pointed out as well.
Weber contrast [C.sub.W] is ratio of task and background luminance
difference and background luminance
As the background luminance
[L.sub.b] is the same for both conditions, then this equation reduces to:
The latter is the estimated sensitivity of the pilot's eyes as derived from the measured background luminance
. When the background is dark, the eye is sensitive to sources of low intensity light, and vice versa.
In general the effect of glare will increase when the source luminance increases, the background luminance
decreases, and the angle between the line of sight and the direction of the light source decreases (see, e.g., Alferdinck, 1996; Alferdinck & Varkevisser, 1991).