IMPROVEMENTS IN THE METHOD AND APPARATUS FOR DISTRIBUTING AND DIFFUSING POWERFUL LIGHTS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Alexander Pelham Trotter at the
Office of the Commissioners of Patents on the 25th July 1882.
ALEXANDER PELHAM TROTTER of Trinity College Cambridge in the County of
Cambridge "IMPROVEMENTS IN THE METHOD AND APPARATUS FOR DISTRIBUTING
AND DIFFUSING POWERFUL LIGHTS."
When a light such as that of an electric lamp or of a brilliant burner is so
powerful that it cannot comfortably be looked at, it is usual to soften it by the use
of opal or other partly opaque glasses, by which a large portion of the light is
wasted. Moreover when such powerful lights are employed for illuminating large
areas, the space in the immediate neighbourhood of the light may be brilliantly'
lighted while the more distant portions of the space are comparatively dark. My
invention relates to improved means of softening powerful lights without great loss
of light and of distributing the illumination with comparative uniformity over
considerable areas, and I effect both these objects by the use of transparent glass so
shaped or moulded on its surface as to diffuse or to distribute or both by refraction
and reflection the rays proceeding from the source of light. I will describe as an
example, a forin of glass lantern which I employ for distribution of such a light as
that from an electric lamp. The general shape of the lantern is that of an inverted
cone, the light being situated at or near the centre of its base. The exterior
surface of the cone is circularly grooved so as to present a series of steps each of
which has its surface so curved that the rays of light passing through it are
distributed by refraction uniformly over the desired extent of area extending
around the lamp. The stepping may be formed on the interior surface of the glass
or partly on the interior and partly on the exterior. Above the cone I provide a
reflector of such curvature that the rays are uniformly distributed by reflection
from it. Between the base of the cone and the reflector a glass cylinder may be
placed having its surface circularly grooved like that of the cone to give uniform
distribution. Instead of employing a cone, a glass of hemispherical or approximately
hemispherical form may be employed the curvature of its steps being varied to suit
the particular angle of incidence of the rays. Instead of employing a conical or
spherical form having a circle for its base, the form may be modified by generating
it on a polygonal base. When it is desired to distribute principally in two opposite

page_text: directions as for example for illuminating a foot pavement or railway platform,
I make the lantern of an elliptical or approximately elliptical form in plan. When
it is desired to diffuse or soften the light as well as to distribute it uniformly
I break up the steps into a number of segments which project from the general
surface with curvatures arranged in plan as well as in section to effect distribution.
When diffusion only without regard to distribution of the light is desired,
projections from the surface or depressions in the surface are formed as solids
of revolution or conoids having curvature such as to refract the rays passing
through them uniformly through a considerable angle in all directions. The
arrangements for distributing and diffusing may be combined by forming the
distributing steps on the exterior and forming diffusing flutings on the interior of
the glass or conversely.