Civil Engineering Reference
In-Depth Information
accommodation (in diopters) of the
lens in the eye, and the refractive error.
from the eyes to the various task elements. Eyeglasses that are tailored to the conditions
at work can then be prescribed.
The limited range of clear vision makes it necessary that items in a workplace are put
at a distance where they can be seen clearly. In the same way that forward functional
reach limits the physical organization of a workspace, so does forward functional vision.
The second most important effect of age is the clouding of vision. In the vitreous
humor, between the lens and the retina, there are particles and impurities. With age these
impurities increase in size. They impair clear vision, because they scatter incoming light
over the retina. Older persons are therefore particularly sensitive to glare sources or stray
illumination, which add a veiling luminance (a cloud) over
FIGURE 4.13
Indirect glare (A) arises
from reflected light, while direct glare
(B) arises directly from the light
source.
the retina (Wright and Rea, 1984). As a result, the contrast on the retina decreases. For
older persons it is therefore important to minimize stray illumination and glare that is not
part of the task (Figure 4.13).
Direct glare comes from light sources, such as overhead luminaries, that are shining
directly into the operator's eyes. The reflected or indirect glare is from light that is
reflected in the workplace from glass or plastic covers, shiny metal, or key caps on a
keyboard. One way of solving the problems of both direct and reflected glare is to use
task illumination. This involves directing lamps with a restricted light cone towards the
visual task. Some examples of task lights are shown in Figure 4.14 (Carlsson, 1979).
