US2897346A - Electric lanterns - Google Patents

Description

.lilly 28, 1959 Filed Jung 28, 1955 R. W. STEVENS ELECTRIC LANTERNS 2 Sheets-Sheet 1 er; y

July 28, 1959 R. w. sTEvENQs 2,897,346

ELECTRIC LANTERNS med June 2e, 1955 2 sheets-sheet a AT1-@wey ELECTRIC LANTERNS Richard William Stevens, London, England `Application `lune 28, 1955, Serial No. 518,605

Claims priority, application Great Britain June 29, 1954 1 Claim. (Cl. 240-25) The present invention relates to electric lanterns -for use with elongated electric lamps, such for example as fluorescent lamps or sodium lamps.

It has for its object to provide an improved lantern, suitable for street lighting which enables a satisfactory light distribution to be obtained from a light source of the type which is extended in at least the vertical direction. Examples of such sources, which are also extended in one horizontal dimension, are a small plurality of fluorescent tubes arranged one above the other or a U-shaped sodium lamp arranged with the limbs of the U one above the other. The type of distribution required is one in which a minimum of light is directed above the horizontal, a peak intensity is provided between and 20 below the horizontal, and the intensity falls off steadily to a still appreciable -value as the direction approaches the downward vertical. The arrangement of lamps one vertically above another has the advantage that the amount of re-direction of light that has to be eiected by the lantern in order to produce the required distribution is less than with other arrangements. Thus with three fluorescent lamps one above the other, the light intensity emerging directly from the lamps in a downward direction is substantially that of one lamp while that available laterally is that of three lamps.

It is usually desirable that only light emitted above the horizontal be re-directed by the light control system, since the `desired luminous intensities in directions below the horizontal are usuallyV greater than the intensities provided by the source in these directions. The control systemjis designedwto provide the balance. It follows therefore, that the control system will usually be arranged to extend upwards from a position approximately level with the upper part of the source.

Control may be achieved by re-directing the light by refraction or reection. In the latter case it is diicult to arrange for the reectors to intercept an adequate amount of light. In the former case, the control system often consists of a transparent panel having, on one or both sides, a number of prisms running parallel to the axis of the source. The diiculty mentioned above as met with reflecting systems kdoes not arise, but there is another difficulty which it is the purpose of this invention to overcome. This is that, when the source is of the type specified having substantial vertical depth, and when the prisms are all of the refraction type, if light from the upper part of the source is directed into the main beam, i.e. in the direction of maximum intensity at 10 to 12 degrees below the horizontal, then the light from the lower parts of the source tends to be directed above the main beam. On the other hand, the amount of light from the lower part of the source intercepted by the refractor panel, is often relatively small and losses are high due to the large angles of incidence involved, so that if the panel is designed to direct light from this part into the main beam, the system is rather ineicient f. ICC? even if the light from the rest of the source is directedl below the main beam.

According to the present invention a lantern for use with a light source of the type set forth comprises refractor panel including prisms running horizontally, at least the upper prisms, and preferably all or nearly all'.

` the prisms, being adapted to direct light from the light v panel, if light from the upper part of the source is directed into the main beam, light from the other parts can be arranged to be directed below it.

The invention is of particular value where the light source is of large dimensions relatively to the panel, or more precisely where, measured in a vertical plane, the ratio of the distance along a line between the centre of the panel and the centre of the light source to the dimension of the light source between planes parallel to the said line is 3 or less.

The terms horizontal and vertica are used in this specification for clearness and simplicity in order to dene the relationship between the dimensions of the source and the refractor panel and it is to be understood that the lantern according to the invention may be used with the prisms running other than horizontally.

The invention will be described by way of example with reference to the accompanying diagrammatic drawings in which:

Fig. 1 shows the relative dispositions of a lantern according to the invention and three fluorescent tubes to be used therewith,

Fig. 2 is a View of the inside of one of the Fig. 1,

Fig. 3 is an enlarged sectional view of the lower left panels in i hand corner of the lantern in Fig. 1,

Fig. 4 is a much enlarged view showing the shapes of the prisms used in each of the tive zones 1 to 5 in Fig. 1, the prisms in'Fig. 4 being correspondingly num bered, and indicates typical light paths, and Y Fig. 5 shows 'a preferred modication of the lantern of Fig. 1 for use with a sodium lamp.

Referring to Figs. l to 4, the lantern has two panels 10 and 11 of Perspex (registered trademark) about 81/2 inches apart and is of rectangular shape with rounded corners. Each panel measures 18 inches x 4% inches vertical depth. The prisms are in five zones (1 to 5 in Fig. l) in each of the two panels, the vertical. depths; of the zones 1 and 2 being approximately equal and` these two zones extending over approximately half thevertical depth of the panel. Zones 3 and 4 are of ap.

proxirnately equal depth and zone 5 has a depth which is about a half of that of the zone 4. The bases 12 of` the prisms in the two upper zones 1 and 2 of each panel' lie in a plane inclined inward and upward at 10 to the vertical. The bases 13 of the prisms in the three lowest;

zones 3, 4 and 5 of each panel lie in a plane inclined downward and inward at an angle of 5 to the vertical., As shown in Fig. 4, the upper surfaces 14 of all the` prisms in the upper four zones are ararnged to reectz the light falling on them from the source. These surfaces are inclined downward and outward at angles of` 1, 6, 12 and 12 respectively proceeding from the` uppermost prism downward. Downward and upward in-` clinations are of course with respect to the horizontal.-

The.. prisms. in theA twomupper.l zonesk 1. and. 2 have each` only one further surface, namely the lower surface 15 through which lightY is passed after reflection at the upper surface, the light being refractedinpassing-.through the lower surface. These lower surfaces are inclined upward andoutward at 29.5 and:22;2- respectively-iu the zones 1` andy 2. The prismsin zones 3.. and 4=each-have two. mutually-inclined lower surfaces- 176 andA 17 through the outer one 16 of which light-reflectedfrom the-upperA surface 14 passes and is refracted. The lower'a surfaces 17 nearer theV centre of the lantern in both zones are inclined upward' and outward at 29. The surfaces 1 6.A

in zones 3` and-4fare shorter thanthe surfaces- 17-1 and:

are inclined upward and outward yat` 25.6- and 38:7'PC respectiyely.

The refractingprisms in the lowestzone havel upper surfaces 18 inclinedY downward and outward at 55.11 andlower surfaces 19 inclined upward and/outward'. at 21.

'The overall thickness ofthewalls of the panels to-the apices of the prisms is about-inch, the prisms themselves occupying abouthalfof thisthickness. The vertical depths of the'bases of-'the prisms areabout equal for zones 2, 3 and 4, rather larger for zonevland about three times as large as zone 2. in zone S. The bases* abut against one another.l

The light source shown in Fig. 1 is in the form of say three fluorescenttubes 2.0, 2-11 and 22. arranged one vertically above the others and is arranged symmetrically in the lantern with the planeV zrthrough the upper surface of theV source (theyupper-wallof the upper luores` cent tube 20) andthe lower edge ofthepanel 11L rmalring `an-angle of about 15.t0 the horizontal; the said sur? facebeing, as shown, above the saidedge.

It will be seen in Fig. l that the ratio of the distance along the line 2.5 between-the centrefof the panelj-and the centreof theflight source tothe` dimension 26 of.

the light source between planes 2K7 and ZSpaIallel' to the4 line 25 is-large. rI`his-ratio-isi` conveniently made about 2.

With a sodium lamp Z4`thepositions ofithe'refractor panelsy 10 and 11 can advantageously be'modied as in-A dicated in Fig. 5 to increase the areas of the prisrnbases asseen from the light sourcet It is a feature of-the form of panel described that it is possible to do this withoutaltering the direction ofA the-mainbearn. Thus itrnay be. done, as shown, by arranging'thebases of vthefprisnisV j in the lowest three zonesftofb'e verticaland therefore inclining the bases of the prismsinthe first two zones at instead of .10 to thevertical as-previouslydescribed,

` but allot-said lampsbenaPQSitiQHedWth respect tQ-Said:

and arranging. the outer surfaces of. the panels at 5 to the vertical, the remainder of. the design being the same as described with reference to Figs. l to 4.

In either embodiment a diusing reflector may be arranged within the lantern above the uppermost lamp to prevent emission of lightupward and to increase the light emitted downward:

Whilst the invention hasbeenfdescribed with particular reference to ahorizontally disposed light source, it is to be understood that itmay-beapplied equally well to a short source of small'horizontal dimensions and extended only in the 'vertical direction. The refractor may then be of circular cross-sectionwi-th-its axis coinciding with that of the source and the lprisms are then arranged to extend circumferentially.

I claim:

A lighting fixture comprising a refractor panel having a. verticali array,l Aof:horizontala prisms arranged in; au; .11P-

per grgupaudm lower. group. theupper. group-0f priistasl` in said vertical array hannstheirbases--in arlaneain: clined inwardly and; upwardly; to drepflight by tQtel; in-

electrie discharge lamps, each. lamp being. Substantially herizental.. andonly onefofitlxe lamps. inrsaid plurality, being in-.the same ,horizontalplaneas `any of` Said prisms.

refractQr. panelso that at least partof the upward light from. each lamp willf heredirected dawnwardly. byv said prisms whereby, the lamps emit mwst` of. the. direct vlight in..a-.lateraldirectonand theunward component f lsh.tv

above each-,lamp isA reflected down by Seidfprisms.

References Cited in the file of'this patent UNITED STATES PATENTS 2315-1781 Rolph Apr. 26; 1938i 2,436,635 De Bishop Feb.24, 1948i 2347456411 Wince June 28; 1949: 236233160- McPhal Dec. 23, 1952y FOREIGN PATENTS 581,751 Frane- Oct. 2; 1924 250,218-l Great Britain Ian. 6',v 1927 376,831 Great- Britain July 18, 1932- 421,663` Great Britain Dec. 2`8, 1934 5035638 Great-PmitainA .Tune- 19, 1939V 6233435 Great Britain May 17, 1945" 91232281 Germany---- June 10, 1954

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