CA1202284A - Lanterns for area lighting - Google Patents
Lanterns for area lightingInfo
- Publication number
- CA1202284A CA1202284A CA000409373A CA409373A CA1202284A CA 1202284 A CA1202284 A CA 1202284A CA 000409373 A CA000409373 A CA 000409373A CA 409373 A CA409373 A CA 409373A CA 1202284 A CA1202284 A CA 1202284A
- Authority
- CA
- Canada
- Prior art keywords
- lantern
- light
- bowl
- regions
- central area
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
The invention provides a lantern for an area light, particularly one having a cut-off light distribution. A
central area of a transparent or transluscent bowl of the lantern has in alternation externally facing reflecting prisms and flats. There are sufficient flats to transmit at least one third of the vertical light and sufficient proportion of prisms to provide a completely flashed prism bank at the direction of peak intensity which is preferably 60°- 65° from the vertical. The prism bank controls the vertical light, so that the intensity in a vertical 60° cone does not exceed 80% of peak intensity, more efficiently than internal prisms. The flats have the additional advantage of facilitating ease of cleaning.
The invention provides a lantern for an area light, particularly one having a cut-off light distribution. A
central area of a transparent or transluscent bowl of the lantern has in alternation externally facing reflecting prisms and flats. There are sufficient flats to transmit at least one third of the vertical light and sufficient proportion of prisms to provide a completely flashed prism bank at the direction of peak intensity which is preferably 60°- 65° from the vertical. The prism bank controls the vertical light, so that the intensity in a vertical 60° cone does not exceed 80% of peak intensity, more efficiently than internal prisms. The flats have the additional advantage of facilitating ease of cleaning.
Description
Improvements in or relating to lanterns for area li~htin~
The present invention relates to lanterns for area lighting and in partlcular for street lighting. It is the practice to light streets and other roadways with lights, now generally discharge lamp9, mounted in part tran3parent or transluoent housings, called lanterns, on suitable columns or other supports above a street to be illuminated. It will be appreciated that although this form of lighting is more commonly seen in streets it may be u~ed in other circumstances perhaps to illuminate private premise~ both inside and out and ~or that reason it i~
generally descrLbed here as area lighting. All references herein to street lighting are to be taken to be applicable as appropriate ~o other forms of area lighting. Area lighting for streets is generally sub~ect to strict regulations regarding, among other things, intensity and distrlbution of light. This resultq from the appllcation, which is to illuminate the road surface as economically as possible. A road user at night sees objects on the road in silhouette against a bright road surfaceO To provide such illumination a road lantern i3 generally deQi~led to pro~ect light up and down a road, towards and away from an observer. That llght which is directed towards an observer produces glare because the observer 1 9 eyes Qee not only light reflected off the road but al~o direct lisht from the lantern. The direction and intensity of the light from a road lantern determines the glare and also the required spacing of lantern~ for uniform lighting.
~ r J
The present invention relates to lanterns for area lighting and in partlcular for street lighting. It is the practice to light streets and other roadways with lights, now generally discharge lamp9, mounted in part tran3parent or transluoent housings, called lanterns, on suitable columns or other supports above a street to be illuminated. It will be appreciated that although this form of lighting is more commonly seen in streets it may be u~ed in other circumstances perhaps to illuminate private premise~ both inside and out and ~or that reason it i~
generally descrLbed here as area lighting. All references herein to street lighting are to be taken to be applicable as appropriate ~o other forms of area lighting. Area lighting for streets is generally sub~ect to strict regulations regarding, among other things, intensity and distrlbution of light. This resultq from the appllcation, which is to illuminate the road surface as economically as possible. A road user at night sees objects on the road in silhouette against a bright road surfaceO To provide such illumination a road lantern i3 generally deQi~led to pro~ect light up and down a road, towards and away from an observer. That llght which is directed towards an observer produces glare because the observer 1 9 eyes Qee not only light reflected off the road but al~o direct lisht from the lantern. The direction and intensity of the light from a road lantern determines the glare and also the required spacing of lantern~ for uniform lighting.
~ r J
2;~
: 2 ~ typical ~peci~ication for road lightlng lantern~ i9 BS.4533 Part 2 o~ ~hich 3ection 2.7 cla~ifie~ group A lantern photometrlc performance irto two categories. One category (cut-oef di~tribution) provid~ better gl ~ control and a lower beam in elevation than the other (~emi-cut-or~ dlqtribution).
The cut-of~ diqtribution allcw3 the beam~q to extend to an ele~ation of 65~ with an intensity at 9D in elevation (ln the vertical plane parallel to the street axls) of 15cd~klmO
The semi-cut-off allows the beam to extend to an elevation of 7~ and the irten~ity at 90 in elevation to be 75 cd/klm.
Thi~ inten~ity limit at ~0 in elevation is an approximate mea~ure of glare and, it can be ~ee~, may be five time~ higher in 3emi-cut-cf~ tha~ in cut-off lantern~. In general lt i~ 30 more e~pe~sive to illuminate a road with cut-off lanter~s compared with ~emi-out-o~f, since the cut-of~ distribution, ~aving a lG~er beam angle, requireq clo~er qpacing ~or acceptable lig~ting unifcrmity.
~ u~ther requirement whdch applies to both diqtributioDs i8 that t~e ~ um inten~it~ wlthin the cone ~rom the downward vertical to an ele~ation o~ 30 should not exceed 80% of the peak inten3ity (or ae the maximum within the beam). It is with compliance w~th thi~ requirement that this invention is concerned.
It ha~ been the practice to obtain the appropriate distribution by the choice of lantern design. A lantern generally includes two parts, a transparent or tra~slucent bowl - ~2g:~Z~
facing the surface to be illuminated, and an opaque canopy above, with the discharge tube or tubes mounted therein. The lantern may include reflectors and the bowl may include shaped 3urfaces to refract the li~ht.
In gener~l a cut-off di~tribution is obtained frcm a lantern including reflectors. In such an optical design, light is refleoted off reflectors on both sides of the lamp to pass underneath and around the end of the lamp. Thi3 requires a relatively large lantern, to include the reflectors, ccmpared with a refractor type of optical design in which light i9 e~itted from the lantern through prism bands on either 3ide of the lamp integral with the lantern bowl. ~owever~ since in gener~l refractor optics produce more glare than refleotor control, it ha3 been usual to reserve refractor optics for 3emi-cut-off di~tribution~.
It i~ an object o~ this invention to provide an improved optical design far area lighting lantern~ for the control of inten~ity direoted vertically downwards fra~ the la~p, substantially within a 30~ Cone. Thi3 i3 partioularly useful for a cut-ofP di~tribution but is al~o appllcable to ~emi-cut-off.
According to the invention there i~ provided a lantern, for an area light, including a transparent or translucent bowl having a generally pla~ar or 3hallcw1y curved part generally perpendicular to a central plane of ~ymmetry of the lantern, ~aid part including a sub~tantially central area having a plurality of regions, acting a external reflecting prism~ to : 4 ~ light pa~si~g therethrough, spaced by substantially flat reglon~.
In order that the inventlon may be clearly under~tood and readily carried with effect it will now be described by way o~
example with reference to the accompanying drawings, if whichs Figure 1 sho~ the centr~l region of le bowl of a prior art lantern, Figure 2 shows the same region o~ a lantern in accordance with the invention, Flgure 3 show~ an alternative form of the pri$ms 5 of Figure 2 and, Figure 4 shows a complete lantern in accordance with the invention.
Thi~ deq~ription o~ the invention will be in relatior to a new desig~ of lantern providing cut-off di~tribution by purely refractive opti~al design. It 3hould be noted, however, that the optical de~ign for control o~ the vertical light inten~ity iY applicable both to cut-o~f de~igns using re~lector3 and semi-cut-off designs.
In general ~uch lanterns are mounted to illuminate a ~ 20 surfaoe directly there belcw. H~wever the lanterns may be mou~ted ln other positions. In thi~ specification the words vertic~l and horlzontal are considered to have that relationship to the lantern~ however it is mounted, which they would have wher. the la~p i3 mounted conventionally above level ground with the vertical axis perpendicular to the illuminated surface.
: 5 ~ onsiderirg an e~isting arrangement giving semi-cut-o~r distribution ~or a typical di~charge lamp, a 135 Watt SOX (low pre~sure sodium)-lamp, the lantern comprise~ a white glass reinforced plastic (GRP) canopy with a clear pri~matic bowl below. The existin~ semi-cut-off ver~ion has a shallow canopy with a semi-circular cro3~-section of bowl. In comparlson the cut-off development has a deeper canopy with a shallower bowl havi~g a relatively flat prismatic base and clear and nearly vertical sides. Since refractor o~ly optic~ are used the overall QiZe is smaller tha~ ~or conventional reflector de~igns, and has lower material coYt~.
The bowl is de~igned to be a~ ~hallow as po~sible to keep the pro~ected area ~rom the side in the horlzontal direction to a minimum. Thi~ help to reduce horizontal ligh b intensity due to light scattered i~ the bowl material In con~unction with this the bowl is expected to have sufficient flashed projected area tdefined a3 an area projecting an image of the light ~ource) in the direction of a peak, which should produce a minimum inten~ity of 200 cd~100D lamp lumens in a region between 60 and 65 from the do~nward vertical.
As mentioned hereinbefore, an important requirement with which this invention is concerned is that of limiting the downward intensity to les3 than 80~ of the peak intensity.
In achieving this requirement problems ari~e because of the flat and shallol~ nature of the bowl of which the pro~ected area iq ~ignificantly greater ir the 0 to 30 region than when ~219ZZ8~
: 6 ~Lewed from 65~.
Figure 1 show~ in cros~section perpendicular to the principal a~Ls of the lamp, the centre part of the bowl Or a prior art cut-o~f lantern. Over most of the bottom of the howl there are formed internally facing prisms 1 which extend substantially ~or the complete length of the bowl. ~he light falling on such prisms becomes increasinsly less effectlve when it strike~ them from closer to the ~ertical a~i~ 2. This axi8 9 which i9 usually vertical in relation to the street surface, is in fact the central plane of symmetry of the lankern but ~ill be called the vertical axis herein. As a re~ult there is too much light in the doT~nward direction compared with that in the direction of,pe;ak inten~ity.
To correot this to some extent, in a central region AA the prisms are repliqced by ~emi-circular grooves 3 which scatter rather than oontrolling the light from the lamp. The aim is then to ~catter a suf~icient amount of light out of the 0 to 30 cone. Some li~ht paths 4, from the lamp, are ~hown to clarify the optLcs o~ the de~igns.
It isS however, ~ound that this is still not as effective as would be desired and Figure 2 shows the same cross section as Figure 1 but incorporating the improved optical de~ign of this invention. Pr:Lsms 1 are provided as before but in the centre the in ide grOQ~es 3 have been replaced by prism~ 5 on the outside of the bowl. These prisms 5 are reflecting prisms ~ince a light ray entering a pri~m will be internally reflected, as well as bei~g reYracted be~ore lea~ing the prism. This can be seen with a ray bet~een limit3 6 and 61, of which 41 i~
typical, which is reflected in pri~m 51 a3 shown. In pri~mq 1 in contra3t there is only refraction. Between eaeh prism 5, including the terminatin~ half prisms 5 ~ there ls a flat region 7. Some light, such a~ that of ray 42 passes ~traight through the flats 7, giving a vertical beam, while tho3e, such as 43 and 44, paSstng through the prism~ 5 are largely reflected out cf the vertical beams.
The ratio Or pri3ms 5 to flats 7 in area may be varied to adjust the intensity of the vertical beam but the prisms 5 Qhould be sufficiently closely spaced to give the appearance of a completely flashed pris~ bank in the direction of the main beam (that is, at the peak). It is preferred that 3 of the vertical light beam pa3se3 through ~lat3 7. An additional advantage resulting ~rom the pre3ence of the flats 7 is in eaQe of cleaning of the bowl exterior.
Certain considera~ions should preferably be met in the design of these pri~ms 5. The external surface B of the bowl i~ ~ubstantially flat but is in thi~ e~ample a shallow curve.
If a chord to this curve is as shown at 9, acro~s the prisms 5, it i3 preferred that the tops of the prisms do not protrude beyond thi~ chord 90 as to reduce the risk of 3pill light being refracted out at 90 . The ir~er surface 10 above prismQ 5 is alQo preferred to be parallel to chord 9 or at least to not deviate from paralleli~m by more than about 5. It may also z~
: 8 be curved provided the maximu~ deviation from the side of the arc to the bottom doe~ not exceed about 5O
Although triangular prisms with intervening flats have been illustrated in Figure 2 it will be understood that the lnvertion may be imple~ented, with ~ome loss of performance, by shapes which approxim'ate to that ideal. ~or example Figure 3 illustrates how the pri~m~ ma~ ~e approximated by grooves or flutes 11 with concavities outward facing. The top most parts of these tend 'to act as flats 7 while the regions o~ the cu~ps 12 tend to act a9 reflecting prisms. Such grooveq do, however, tend lo scatter the light as oppo~ed to controlling it and are not preferred.
Figure ~ shows in cross-section a complete cut-off lantern in accordance 7~th the invention. A 135 watt SOX lamp 13 having a U-shaped discharge tube 14 is enclo~ed in the lantern which comprise~s a eanopy 15 and bowl 16. The two are clipped together by convent1onal means (not shown) and sealed with a sealing pad 17 to exclude moisture. Other features are identified by t;he same reference numerals a~ in the earlier Figures. The lamp illustrated is 775mm long 67mm dia. The length of the lantern (perpendicular to the Figure) is generally slightly longer than the tube in u3e. All dimensions olearly may vary with t;he application and powers of the lamp. It is preferred that the prisms 5 extend for ~ubstantially the full length of the lantern. They may, however, merely extend only over a suf~icient region to achieve the desired 80~ intensity.
- ~l2~
: 9 The remainder of the central region may be provided wlth internal ~rooves 3 as shown in Figure lo Although the ratio of the width WAof the exterior prism region to the width ~B of the totaL lantern7 should be ad~usted for Ibest results it iq in practice a ratio which varies for different designs and lamps. I~ general it should be ~ adjusted so tlhat the pris~s 5 have a ~ufficient lnte~ception o~
the 0-30 be~ but ~aries with the application.
The inve~tion has been described in terms o~ a lantern for a low pressure sodium light having a linear tube to which the external reflecting prisms are parallel. It will be appreciated that it is applicable to other ~or~ of lamp. For example ~erc~y lamps and some high pre~sure sodium (SON) lamps ~eneraLly have~ elliptical outer envelopes. These are o~ten used with ~ore rounded shapes of bowl. In application of this inventiorl that; bo~l s~ape could be used with the external ren ecting pr~ sms in cur~ed disposition generally concentric around the lamp. Other shapes can be devised to suit other lamp cor~igur~ltior~.
: 2 ~ typical ~peci~ication for road lightlng lantern~ i9 BS.4533 Part 2 o~ ~hich 3ection 2.7 cla~ifie~ group A lantern photometrlc performance irto two categories. One category (cut-oef di~tribution) provid~ better gl ~ control and a lower beam in elevation than the other (~emi-cut-or~ dlqtribution).
The cut-of~ diqtribution allcw3 the beam~q to extend to an ele~ation of 65~ with an intensity at 9D in elevation (ln the vertical plane parallel to the street axls) of 15cd~klmO
The semi-cut-off allows the beam to extend to an elevation of 7~ and the irten~ity at 90 in elevation to be 75 cd/klm.
Thi~ inten~ity limit at ~0 in elevation is an approximate mea~ure of glare and, it can be ~ee~, may be five time~ higher in 3emi-cut-cf~ tha~ in cut-off lantern~. In general lt i~ 30 more e~pe~sive to illuminate a road with cut-off lanter~s compared with ~emi-out-o~f, since the cut-of~ distribution, ~aving a lG~er beam angle, requireq clo~er qpacing ~or acceptable lig~ting unifcrmity.
~ u~ther requirement whdch applies to both diqtributioDs i8 that t~e ~ um inten~it~ wlthin the cone ~rom the downward vertical to an ele~ation o~ 30 should not exceed 80% of the peak inten3ity (or ae the maximum within the beam). It is with compliance w~th thi~ requirement that this invention is concerned.
It ha~ been the practice to obtain the appropriate distribution by the choice of lantern design. A lantern generally includes two parts, a transparent or tra~slucent bowl - ~2g:~Z~
facing the surface to be illuminated, and an opaque canopy above, with the discharge tube or tubes mounted therein. The lantern may include reflectors and the bowl may include shaped 3urfaces to refract the li~ht.
In gener~l a cut-off di~tribution is obtained frcm a lantern including reflectors. In such an optical design, light is refleoted off reflectors on both sides of the lamp to pass underneath and around the end of the lamp. Thi3 requires a relatively large lantern, to include the reflectors, ccmpared with a refractor type of optical design in which light i9 e~itted from the lantern through prism bands on either 3ide of the lamp integral with the lantern bowl. ~owever~ since in gener~l refractor optics produce more glare than refleotor control, it ha3 been usual to reserve refractor optics for 3emi-cut-off di~tribution~.
It i~ an object o~ this invention to provide an improved optical design far area lighting lantern~ for the control of inten~ity direoted vertically downwards fra~ the la~p, substantially within a 30~ Cone. Thi3 i3 partioularly useful for a cut-ofP di~tribution but is al~o appllcable to ~emi-cut-off.
According to the invention there i~ provided a lantern, for an area light, including a transparent or translucent bowl having a generally pla~ar or 3hallcw1y curved part generally perpendicular to a central plane of ~ymmetry of the lantern, ~aid part including a sub~tantially central area having a plurality of regions, acting a external reflecting prism~ to : 4 ~ light pa~si~g therethrough, spaced by substantially flat reglon~.
In order that the inventlon may be clearly under~tood and readily carried with effect it will now be described by way o~
example with reference to the accompanying drawings, if whichs Figure 1 sho~ the centr~l region of le bowl of a prior art lantern, Figure 2 shows the same region o~ a lantern in accordance with the invention, Flgure 3 show~ an alternative form of the pri$ms 5 of Figure 2 and, Figure 4 shows a complete lantern in accordance with the invention.
Thi~ deq~ription o~ the invention will be in relatior to a new desig~ of lantern providing cut-off di~tribution by purely refractive opti~al design. It 3hould be noted, however, that the optical de~ign for control o~ the vertical light inten~ity iY applicable both to cut-o~f de~igns using re~lector3 and semi-cut-off designs.
In general ~uch lanterns are mounted to illuminate a ~ 20 surfaoe directly there belcw. H~wever the lanterns may be mou~ted ln other positions. In thi~ specification the words vertic~l and horlzontal are considered to have that relationship to the lantern~ however it is mounted, which they would have wher. the la~p i3 mounted conventionally above level ground with the vertical axis perpendicular to the illuminated surface.
: 5 ~ onsiderirg an e~isting arrangement giving semi-cut-o~r distribution ~or a typical di~charge lamp, a 135 Watt SOX (low pre~sure sodium)-lamp, the lantern comprise~ a white glass reinforced plastic (GRP) canopy with a clear pri~matic bowl below. The existin~ semi-cut-off ver~ion has a shallow canopy with a semi-circular cro3~-section of bowl. In comparlson the cut-off development has a deeper canopy with a shallower bowl havi~g a relatively flat prismatic base and clear and nearly vertical sides. Since refractor o~ly optic~ are used the overall QiZe is smaller tha~ ~or conventional reflector de~igns, and has lower material coYt~.
The bowl is de~igned to be a~ ~hallow as po~sible to keep the pro~ected area ~rom the side in the horlzontal direction to a minimum. Thi~ help to reduce horizontal ligh b intensity due to light scattered i~ the bowl material In con~unction with this the bowl is expected to have sufficient flashed projected area tdefined a3 an area projecting an image of the light ~ource) in the direction of a peak, which should produce a minimum inten~ity of 200 cd~100D lamp lumens in a region between 60 and 65 from the do~nward vertical.
As mentioned hereinbefore, an important requirement with which this invention is concerned is that of limiting the downward intensity to les3 than 80~ of the peak intensity.
In achieving this requirement problems ari~e because of the flat and shallol~ nature of the bowl of which the pro~ected area iq ~ignificantly greater ir the 0 to 30 region than when ~219ZZ8~
: 6 ~Lewed from 65~.
Figure 1 show~ in cros~section perpendicular to the principal a~Ls of the lamp, the centre part of the bowl Or a prior art cut-o~f lantern. Over most of the bottom of the howl there are formed internally facing prisms 1 which extend substantially ~or the complete length of the bowl. ~he light falling on such prisms becomes increasinsly less effectlve when it strike~ them from closer to the ~ertical a~i~ 2. This axi8 9 which i9 usually vertical in relation to the street surface, is in fact the central plane of symmetry of the lankern but ~ill be called the vertical axis herein. As a re~ult there is too much light in the doT~nward direction compared with that in the direction of,pe;ak inten~ity.
To correot this to some extent, in a central region AA the prisms are repliqced by ~emi-circular grooves 3 which scatter rather than oontrolling the light from the lamp. The aim is then to ~catter a suf~icient amount of light out of the 0 to 30 cone. Some li~ht paths 4, from the lamp, are ~hown to clarify the optLcs o~ the de~igns.
It isS however, ~ound that this is still not as effective as would be desired and Figure 2 shows the same cross section as Figure 1 but incorporating the improved optical de~ign of this invention. Pr:Lsms 1 are provided as before but in the centre the in ide grOQ~es 3 have been replaced by prism~ 5 on the outside of the bowl. These prisms 5 are reflecting prisms ~ince a light ray entering a pri~m will be internally reflected, as well as bei~g reYracted be~ore lea~ing the prism. This can be seen with a ray bet~een limit3 6 and 61, of which 41 i~
typical, which is reflected in pri~m 51 a3 shown. In pri~mq 1 in contra3t there is only refraction. Between eaeh prism 5, including the terminatin~ half prisms 5 ~ there ls a flat region 7. Some light, such a~ that of ray 42 passes ~traight through the flats 7, giving a vertical beam, while tho3e, such as 43 and 44, paSstng through the prism~ 5 are largely reflected out cf the vertical beams.
The ratio Or pri3ms 5 to flats 7 in area may be varied to adjust the intensity of the vertical beam but the prisms 5 Qhould be sufficiently closely spaced to give the appearance of a completely flashed pris~ bank in the direction of the main beam (that is, at the peak). It is preferred that 3 of the vertical light beam pa3se3 through ~lat3 7. An additional advantage resulting ~rom the pre3ence of the flats 7 is in eaQe of cleaning of the bowl exterior.
Certain considera~ions should preferably be met in the design of these pri~ms 5. The external surface B of the bowl i~ ~ubstantially flat but is in thi~ e~ample a shallow curve.
If a chord to this curve is as shown at 9, acro~s the prisms 5, it i3 preferred that the tops of the prisms do not protrude beyond thi~ chord 90 as to reduce the risk of 3pill light being refracted out at 90 . The ir~er surface 10 above prismQ 5 is alQo preferred to be parallel to chord 9 or at least to not deviate from paralleli~m by more than about 5. It may also z~
: 8 be curved provided the maximu~ deviation from the side of the arc to the bottom doe~ not exceed about 5O
Although triangular prisms with intervening flats have been illustrated in Figure 2 it will be understood that the lnvertion may be imple~ented, with ~ome loss of performance, by shapes which approxim'ate to that ideal. ~or example Figure 3 illustrates how the pri~m~ ma~ ~e approximated by grooves or flutes 11 with concavities outward facing. The top most parts of these tend 'to act as flats 7 while the regions o~ the cu~ps 12 tend to act a9 reflecting prisms. Such grooveq do, however, tend lo scatter the light as oppo~ed to controlling it and are not preferred.
Figure ~ shows in cross-section a complete cut-off lantern in accordance 7~th the invention. A 135 watt SOX lamp 13 having a U-shaped discharge tube 14 is enclo~ed in the lantern which comprise~s a eanopy 15 and bowl 16. The two are clipped together by convent1onal means (not shown) and sealed with a sealing pad 17 to exclude moisture. Other features are identified by t;he same reference numerals a~ in the earlier Figures. The lamp illustrated is 775mm long 67mm dia. The length of the lantern (perpendicular to the Figure) is generally slightly longer than the tube in u3e. All dimensions olearly may vary with t;he application and powers of the lamp. It is preferred that the prisms 5 extend for ~ubstantially the full length of the lantern. They may, however, merely extend only over a suf~icient region to achieve the desired 80~ intensity.
- ~l2~
: 9 The remainder of the central region may be provided wlth internal ~rooves 3 as shown in Figure lo Although the ratio of the width WAof the exterior prism region to the width ~B of the totaL lantern7 should be ad~usted for Ibest results it iq in practice a ratio which varies for different designs and lamps. I~ general it should be ~ adjusted so tlhat the pris~s 5 have a ~ufficient lnte~ception o~
the 0-30 be~ but ~aries with the application.
The inve~tion has been described in terms o~ a lantern for a low pressure sodium light having a linear tube to which the external reflecting prisms are parallel. It will be appreciated that it is applicable to other ~or~ of lamp. For example ~erc~y lamps and some high pre~sure sodium (SON) lamps ~eneraLly have~ elliptical outer envelopes. These are o~ten used with ~ore rounded shapes of bowl. In application of this inventiorl that; bo~l s~ape could be used with the external ren ecting pr~ sms in cur~ed disposition generally concentric around the lamp. Other shapes can be devised to suit other lamp cor~igur~ltior~.
Claims (16)
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: `
1. A lantern, for an area light, including a transparent or translucent bowl having a generally planar or shallowly curved part generally perpendicular to a central plane of ymmetry of the lantern, said part; including a substantially central area having a plurality of regions, acting as external reflecting prisms to light passing therethrough, spaced by substantially flat regions.
2. A lantern according to claim 1 in which the regions acting as reflecting prisms are sufficiently closely spaced to provide a completely flashed prism bank when viewed from the direction of peak intensity of the lamp.
3. A lantern according to claim 2 in which the said direction is inclined to the central plane of symmetry by between 60° and 65°.
4. A lantern according to any one of claims 1 to 3 in which the regions acting as reflecting prisms are substantially spaced to allow at least one third of light travelling substantially parallel to the central plane of symmetry to pass through said perpendicular regions.
5. A lantern according to any one of claims 1 to 3 in which the external surface of the bowl has a base part, including said central area, which is substantially flat outside said central area and in which the internal surface of the central area is substantially parallel to said flat part.
6. A lantern according to claim 1 in which the external surface of the bowl has a base part, including said central area, which is convex outside said central area.
: 11 :
: 11 :
7. A lantern according to claim 6 in which the tips of said regions acting as reflecting prisms do not protrude beyond a chord to said convex surface between the extremes of the central area.
8. A lantern according to claim 7 in which the inside surface of said central area does not deviate by more than 5° from parallelism to said chord.
9. A lantern according to any one of claims 1 to 3 in which the regions acting as reflecting prisms. are substantially triangular prisms.
10. A lantern according to any of claims 1 to 3 in which the external surface of said central area is formed with outwardly facing concave flutes of which the cusps are substantially perpendicular to said vertical axis.
11. A lantern according to any ore of claims 1 to 3 in which said regions acting as reflecting prisms are linear and disposed substantially parallel to each other.
12. A lantern according to any one of claims 1 to 3 in which said region acting as reflecting prisms are curved and disposed around the centre of said central area.
13. A lantern, for an area light, including a transparent or translucent bowl whose exterior includes a substantially central area having, in alternation, substantially flat regions and regions protruding from the bowl to function as reflecting prisms.
14. An area light having a lantern according to any of claims 1 to 3.
15. An area light having a lantern according to any one of claims 1 - 3 and arranged to have a cut-off light distribution.
: 12 :
: 12 :
16. A street light including a lantern comprising a position for mounting a lamp, a canopy disposed to be above the lamp position when the light is in use and a transparent or translucent bowl detachably sealed to the canopy to enclose the lamp position, the bowl including a central region, disposed to ? ,beneath the lamp position when the light is in use, the region being substantially flat on the interior of the bowl and comprising on the exterior of the bowl a plurality of recessed reflecting prisms spaced by substantially flat regions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409373A CA1202284A (en) | 1982-08-13 | 1982-08-13 | Lanterns for area lighting |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409373A CA1202284A (en) | 1982-08-13 | 1982-08-13 | Lanterns for area lighting |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1202284A true CA1202284A (en) | 1986-03-25 |
Family
ID=4123397
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000409373A Expired CA1202284A (en) | 1982-08-13 | 1982-08-13 | Lanterns for area lighting |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1202284A (en) |
-
1982
- 1982-08-13 CA CA000409373A patent/CA1202284A/en not_active Expired
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