and the height of the surface of the pavement from the floor of the
basement is 8 feet.
Solution.--Turning to page 238
we select the
upper half of the page corresponding to "basement 30 feet wide;" we
select the "Storage Illumination," and of this table take the third
column and the seventh row corresponding to "length of basement 80
feet;" we here find that we need 178 square feet of multi-prism
sidewalk. This forms a strip of prisms in front of the building
practically six feet wide.
In order to determine the prescription for
the lucidux, turn to page 251 corresponding to the
height of the prism
pavement above basement floor, 8 feet, and to the first column headed
6 feet, because the width of the multi-prism sidewalk prisms is 6 feet.
The prescription for the lucidux, therefore, will be found in the
first column marked 6, and should have a depth of 60 inches, as
indicated in the first left-hand column, in order to get the best
results. Since, however, the lower edge of our beam is 10 inches
below the sidewalk prisms we may discard the upper 10 inches,
consisting of 3 rows of J's of lenses of the lucidux. Our lucidux
will, therefore, consist of 13 rows of prism lenses of the following
prescription, J, K, K, L, L, M, M, N, N, O, O, O, from top to bottom.
The lucidux will be arranged in several pieces of prism plates
appropriately supported, and when complete will run entirely across
the basement. Should it be impossible to install a lucidux of the
indicated depth, reduce the area always by omitting the bottom rows.
COURTS AND LIGHT SHAFTS IN RELATION TO LUXFER PRISMS.
If prism plates are used in connection with the
windows of light courts in office buildings, the dimensions of these
courts may be materially reduced and yet give a much better illumination
to the offices. Whatever the dimensions of the court to which Luxfer
prisms are applied, the light obtained is very greatly improved. In
designing new courts they should, when practicable, be substantially
square and not long and narrow.
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