Improvements in or relating to Lamps for Illuminating Purposes.
Year: 1892

page_text: Date of Application, 24th June, 1892
Complete Specification Left, 17th Mar., 1893-Accepted, 17th June, 1393
PROVISIONAL SPECIFICATION.
Improvements in or relating to Lamps for Illuminating Purposes.
A communication from JEAN BAPTISTE FERDINAND FRÉDUREAU, of 18, Rue
Lafayette, Paris, in the Republic of France, Engineer.
1, ALFRED JULIUS BOULT, of 323, High Holborn, in the County of Middlesex,
Member of the Institution of Mechanical Engineers, do hereby declare the nature
of this invention to be as follows:-
To diffuse or concentrate a series of rays emanating from a source of light and
extending in one or more directions, by means of transparent envelopes or casings,
either of the two well-known principles, viz. refraction or reflection, have to be
taken as a basis of operation.
The principle adopted in constructing light-houses is refraction; reflection may
be applied to practical purposes, either (A) by the employment of surfaces the
selection of which is based upon the principle of the equality of the angles of
incidence and of reflection (reflection by means of a parabolic are is within the
scope of this principle); or (B) by the employment of surfaces arranged according
to the principle of the limiting angle.
For diffusing light at a great distance, as for example, lighthouses are required
to do, the object is to have all the rays emanating from one source of light fall on
the same horizontal plane, and if required in a predetermined direction in such
plane. This object is attained by the employment of non-concentric offset lenses,
the peculiar arrangement of which is intended to avoid the inaccuracies which
sphericity involves. These lenses so break the rays of light as to cause them to lie
in one common horizontal plane.
Where the illuminating effect is to extend but to medium distances, either
refraction, as in the case of lighthouses, or reflection upon a continuous parabolic
surface, as in Mangin's projector, or similar apparatus, may be adopted.
For short distances such as the lighting of streets, yards, works, railway-stations,
places of public resort, and apartments, neither of the two systems mentioned will
give satisfactory results, for in this case it is necessary both to diffuse the light so
as to avoid dazzling the eyesight, and yet to concentrate it in that particular part
of the space or apartment where it is specially intended to fulfil a useful purpose, i.e.
within a cone of light the angle of which varies according to circumstances.
THE PRINCIPLE OF THE INVENTION.
This latter problem is solved by my invention which consists in placing the source.
of light whatever it may be (such as a voltaic arc, an incandescent electric lamp, or
a gas, oil or petroleum burner) within a transparent envelope of glass or crystal
having a surface, incapable of being flattened or straightened out and preferably of
cylindro-spherical, or spherical shape, provided with a series of prismatic rings, the
section of which in a perpendicular plane is that of a prism with plane or curved
surfaces the particular configuration of which is worked out by calculation, these
prismatic rings being so arranged that the centre of the source of light forms their
common focus.

page_text: The transparent envelopes or casings in question are made of glass or crystal and
may be cast, ground or produced by any other method of manufacture usual in
glass and crystal works.
In one form the apparatus may consist of a cylindro-spherical globe or envelope
surrounded by a series of prismatic rings, each of which is generated by the
revolution about the vertical axis of the globe of a prism, the upper surface of
which is parabolic, while its lower surface is perpendicular to the common axis of
these various parabolic surfaces which axis coincides with that of the globe. The
parabolic surfaces are so calculated as to produce the total reflection of the
rays of light. The upper part of the envelope or casing is provided with a groove
or equivalent, enabling a metal sleeve to be fitted thereto for the purpose of
suspending the casing and attaching the source of light. The lower part of the
globe or envelope is open for the admission of air and thus prevents it from being
heated irregularly.
Instead of being cylindro-spherical, the globe may be spherical or hemispherical
with openings at the top and bottom, which shape is more particularly applicable in
connection with a voltaic are having a fixed source of light, which is moreover
situated close to the diametrical horizontal plane of the sphere.
In another form a spherical globe or envelope is surrounded by a series of
prismatic rings, each generated by the revolution of a prism, the upper surface of
which is plane, while its lower surface is plane or curved, about the vertical axis
of the globe. The upper surface of this prism, however, is so arranged that at the
point where this surface meets the surface of the sphere, the perpendicular, forms,
with the rays emanating from the source of light, an angle equal to the limiting
angle corresponding to the substance employed.
The lower surface forms an arc of a circle the ends of which are situated upon
the extension of the ray of the sphere which limits the prism below and the centre
of which is situated on the bisecting line of the said arc. In practice this arc
nearly coincides with the straight line.

page_text: The rays reflected by the upper surface isste from the prism at right angles to
the lower surface, which latter receives no rays of light directly from the source.
A cylindro-spherical globe or envelope may be constructed according to the
same principle as the latter spherical envelope and fulfilling the same condition, viz.
that the central angles intercepted by the prisms both upon the spherical and the
cylindrical portions of the envelope are all equal.
Dated this 24th day of June 1892.
ALFRED J. BOULT,
Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in or relating to Lamps for Illuminating Purposes.
A communication from JEAN BAPTISTE FERDINAND FRÉDUREAU, of 18, Rue
Lafayette, Paris, in the Republic of France, Engineer.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :-
To diffuse or concentrate a series of rays emanating from a source of light and
extending in one or more directions, by means of transparent envelopes or casings,
either of the two well known principles, riz. refraction or reflection, have to be
taken as a basis of operation.
The principle adopted in constructing lighthouses is refraction; reflection may
be applied to practical purposes, either (A) by the employment of surfaces the
selection of which is based upou the principle of the equality of the angles of
incidence and of reflection (reflection by means of a parabolic arc is within the
scope of this principle); or (B) by the employment of surfaces arranged according
to the principle of the limiting angle.
For diffusing light at a great distance, as for example, lighthouses are required
to do, the object is to have all the rays emanating from one source of light, fall
on the same horizontal plane, and if required, in a predetermined direction in such
plane. This object is attained by the employment of non-concentric offset lenses,
the peculiar arrangement of which is intended to avoid the inaccuracies which
sphericity involves. These lenses so break the rays of light as to cause them to
lie in one common horizontal plane.
Where the illuminating effect is to extend but to medium distances, either
refraction, as in the case of lighthouses, or reflection upon a continuous parabolic
surface, as in Mangin's projector, or similar apparatus, may be adopted.
For short distances such as the lighting of streets, yards, works, railway-stations,
places of public resort, and apartments, neither of the two systems mentioned will
give satisfactory results, for in this case it is necessary both to diffuse the light so
as to avoid dazzling the eyesight, and yet to concentrate it in that particular part
of the space or apartinent where it is specially intended to fulfil a useful purpose,
i.e. within a cone of light the angle of which varies according to circumstances.
THE PRINCIPLE OF THE INVENTION.
This latter problem is solved by my invention which consists in placing the
source of light whatever it may be (such as a voltaic arc, an incandescent electric
lamp, or a gas, oil or petroleum burner) within a transparent envelope of glass or
crystal having a surface, incapable of being flattened or straightened out and
preferably of cylindro-spherical, or spherical shape, provided' with a series of

page_text: The transparent envelopes or casings in question are made of glass or crystal
and may be cast, ground or produced by any other method of manufacture usual in
glass and crystal works.
In one form the apparatus may consist of a cylindro-spherical globe or envelope
surrounded by a series of prismatic rings, each of which is generated by the
revolution about the vertical axis of the globe of a prism, the upper surface of
which is parabolic, while its lower surface is perpendicular to the common axis of
these various parabolic surfaces which axis coincides with that of the globe. The
parabolic surfaces are so calculated as to produce the total reflection of the rays of
light. The upper part of the envelope or casing is provided with a groove or
equivalent, enabling a metal sleeve to be fitted thereto for the purpose of suspending
the casing and attaching the source of light. The lower part of the globe or
envelope is open for the admission of air and thus prevents it from being neated
irregularly.
Instead of being cylindro-spherical, the globe may be spherical or hemi-spherical
with openings at the top and bottom, which shape is more particularly applicable
in connection with a voltaic are having a fixed source of light, which is moreover
situated close to the diametrical horizontal plane of the sphere.
In another form a spherical globe or envelope is surrounded by a series of
prismatic rings, each generated by the revolution of a prism, the upper surface of
which is plane, while its lower surface is plane or curved, about the vertical axis
of the globe. The upper surface of this prism, however is so arranged that at the
point where this surface meets the surface of the sphere, the perpendicular, forms,
with the rays emanating from the source of light, an angle equal to the limiting
angle corresponding to the substance employed.

page_text: The lower surface forms an arc of a circle the ends of which are situated upon
the extension of the ray of the sphere which limits the prism below and the centre.
of which is situated on the bisecting line of the said arc. In practice this arc.
nearly coincides with the straight line.
The rays reflected by the upper surface issue from the prism at right angles to
the lower surface, which latter receives no rays of light directly from the source.
A cylindro-spherical globe or envelope may be constructed according to the
same principle as the latter spherical envelope and fulfilling the same condition,.
viz. that the central angles intercepted by the prisms both upon the spherical and
the cylindrical portions of the envelope are all equal.
In the accompanying drawings I have shown sections of five different forms of
lamp globes or casings constructed according to this invention.
Figures 1 and 2 show a cylindro-spherical globe or envelope which is surrounded.
by a series of prismatic rings, each of which is generated by the revolution about.
the vertical axis of the globe of a prism, the upper surface of which is parabolic,
while its lower surface is perpendicular to the common axis of these various:
parabolic surfaces which axis coincides with that of the globe. The parabolic
surfaces are so calculated as to produce the total reflection of the rays of light
emanating from the point F which is the common focus of all the parabolic upper
surfaces. The upper part of the envelope or casing is provided with a groove or-
equivalent enabling a metal sleeve to be fitted thereto for the purpose of suspending
the casing and attaching the source of light. The lower part of the globe or
envelope is open for the admission of air and thus prevents it from being heated
irregularly.
Figure 3 shows a spherical or approximately spherical globe or envelope.
constructed according to the same rules as the first form. The point F is the-
common focus of all the parabolic upper surfaces of the rings surrounding the
globe. It has wider openings at the top and bottom and more particularly
applicable in connection with a voltaic are having a fixed source of light which is
moreover situated close to the diametrical horizontal plane of the sphere.
Figure 4 shows a spherical globe or envelope which is surrounded by a series of
prismatic rings, being also each generated by the revolution of a prism, having
plane or curved surfaces, about the vertical axis of the globe. The upper surface
of this prism is so proportioned as to produce the total reflection of the rays of
light emanating from the focus F; it is generally plane and so arranged that at.
the point N where this surface meets the surface of the sphere, the perpendicular,.
forms, with the rays emanating from the source of light F, an angle ẞ equal to the
limiting angle corresponding with the substance employed.
When the upper surface is plane the angle ẞ formed by a ray of light F N¹.
emanating from the source of light F with the perpendicular to this upper surface
at the point N is always larger than the angle ẞ; total reflection will therefore:
take place upon the whole surface.
The lower surface of the rings, for instance a b forms an arc of a circle the ends.
of which are situated upon the extension of the ray of the sphere which limits the
prism below and the centre of which is situated on the bisecting line of the said
In practice this are nearly coincides with the straight line.
arc.
The central angles a intercepted by the prisms on the surface of the envelope:
are all equal.
The rays reflected by the upper surface issue from the prism at right angles.
to the lower surface, which latter receives no rays of light directly from the-
source.
Figure 5 is a cylindro-spherical globe or envelope constructed according to the.
same principle as the spherical envelope shown by Figure 4 and fulfilling the same-
condition, viz. that the central angles a intercepted by the prisms both upon the-
spherical and the cylindrical portions of the envelope are all equal. F shows the:
position of the focus.

page_text: Having now particularly described and ascertained the nature of the said
invention. as communicated to me by my foreign correspondent, and in what
manner the same is to be performed, I declare that what I claim is,-
1. The application of the principle of reflecting by means of a transparent
surface rays emanating from a source of light for the double purpose of
concentrating the rays in the shape of an illuminating cone and diffusing part of
such rays by causing them to pass through the said surface.
2. The application of the principle of dispersion for the purpose of modifying
the tone or shade of the rays of light by the deviation of the most refrangible rays.
3. The simultaneous application of the principles of reflection and dispersion by
the arrangement around the source of light of a transparent envelope of glass or
crystal obtained by grinding or moulding presenting the whole or part of a non-
developable surface more especially of cylindro-spherical spherical or hemispherical
shape and provided externally with a series of prismatic parallel circles or rings
which if examined in section on a plane passing through their common axis present
the shape of prisms with curved or plane surfaces the said common axis passing
through the source of light enclosed in the transparent envelope.
4. A lamp globe or casing constructed substantially as described and illustrated
in Figure 1 of the accompanying drawings.
5. A lamp globe or casing constructed substantially as described and illustrated
in Figure 2 of the accompanying drawings.
6. A. lamp globe or casing constructed substantially as described and illustrated
in Figure 3 of the accompanying drawings.
7. A. lamp globe or casing constructed substantially as described and illustrated
in Figure 4 of the accompanying drawings.
8. A lamp globe or casing constructed substantially as described and illustrated
in Figure 5 of the accompanying drawings.
Dated this 17th day of March 1893.
W. P. THOMPSON & BOULT,
Agents for the Applicant.