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ESLA Bi-Multi Group "AL" Two-Way 170°

Genre: Wing type lantern

The wing type lantern was invented by Haydn Harrison in the early 1920s. Typified by its simple construction and unique shape, Harrison's design collected some of the flux emitted by the upper parts of a symmetrical point light source, and fashioned it into various beams which were used to illuminate the road surface. The flux emitted in the lower hemisphere of the light source was uncontrolled, producing a circular pool of light below the lantern. Therefore the lantern illuminated both the road surface and its immediate environment.

The wings of the lantern controlled the number and angles of the beams. Given the huge number of different lighting requirements of roads and their environs, a large number of differently configured wing type lanterns were produced. These differed in the number of wings and the angles of the beam; it wasn't uncommon to find many different lanterns lighting a single stretch of road.

The first type of wing lantern, due to Harrison, used facetted, mirrored glass pieces stuck to a cast-iron frame (and he held the patent for the method of arranging and sticking them). Other manufacturers also produced wing type lanterns; but elected to use polished enamel surfaces, curved etched and fluted glass, and/or glass strips held by metal lugs in order to side-step the patent.

Whilst the utilization factor was lower than other lanterns (due to little flux being collected above the lantern), and glare from the totally exposed bulb was an issue, wing type lanterns became popular for their sheer robustness, minimal number of parts and cheapness.

The design of the wing type lantern changed little over the next thirty years. Although open lanterns were frowned upon by the mid-1950s (as no protection was afforded to the bulb nor the reflective surface so both got dirty and required regular cleaning), wing type lanterns were still being installed in the 1960s; but in the end, discharge lamps and the benefits of enclosed lanterns saw their eventual downfall.


Name: ESLA Bi-Multi Group "A" Two-way 170°
Date: Circa 1920s - 1950s
Dimensions: Length: 12 ¼", Width: 11 ¼", Height: 10 ½"
Light Distibution: Non Cut-Off Distribution (MOT Report 1937)
Lamp: 40-200W GLS




History

The Bi-Multi, the first wing-type lantern, was invented in 1923 by Haydn Harrison. Unable to find a manufacturer for his new lantern, he approached schoolfriend Herbert Biggleston who owned a foundry in Canterbury. Electrical Street Lighting Apparatus (ESLA) was founded shortly afterwards.

The Bi-Multi was a revolution. All the other manufacturers were making over complex, multiple part frame-type lanterns, modifications of early gas style fittings. Harrison's genius was to simply remove all the complexity and reduce a lantern to a bulb, focusing mechanism and simple reflective optical system.

As epitomized by the wing type lanterns, the original Bi-Multi was made in many variants, each characterized by different number of wings and different beam angles. This allowed lighting engineers to select lanterns for specific sections of road, especially for bends, dead-ends and road junctions.

In this era before any standardization and/or conformity of mounting heights and spacing, the original Bi-Multi was a small lantern, designed to cast a narrow, intense beam as directed by each wing. This allowed roads to be lit under varying conditions with a minimal number of lanterns; but the intensity ratio was excessively high and glare was a constant problem.


The first British Standard (BS 307:1927) did nothing to improve matters; but the coming of the MOT Report (1937) finally standardized mounting heights and spacing, and Harrison was able to change the optical system of the Bi-Multi to reduce the intensity ratio and create a wider beam. The result was the larger Bi-Multi Group "AL" (with the original Bi-Multi system becoming the Group "A").


As bulb wattages increased, a Group "B" lantern was introduced to light Group "A" roads (suggesting that Harrison's lantern predated the standard naming of the MOT Report). Twin lamp version also appeared, but were only used for special circumstances.




Popularity

Being rugged, simple and cheap, the Bi-Multi system was extremely popular, and these characteristic facetted lanterns could be found all over the country. They were especially popular both with the suburban expansions of the cities being built in the 1930s, and various Parish Councils who needed a cheap, effective, and above all, simple lantern.

Their popularity waned in the 1950s with the coming of discharge lamps and enclosed lanterns, and the energy crisis of the 1970s saw large numbers being removed. Whilst only a handful on exist on the public highway, they have become highly sought after by enthusiasts, and the Bi-Multi has become a collector's item.




Identification

The ESLA Bi-Multi is easily identified by its glass facets. If a lantern has three rows of mirrored glass facets then it's an ESLA. Further identification is provided by the makers name, angular schedule, and patent numbers on the canopy of the lantern. In early lanterns, this is scribed into the wings (requiring paint removal to see them); on later lanterns, these are cast as raised letters (rare) or raised letters on blocks.




Optical System

The optical system of the ESLA Bi-Multi was based on a series of intersecting parabolas with the bulb at the focal centre. The top half of the parabola was fashioned into a reflective surface using facetted mirrors. The flux collected by the mirrors was then fashioned into a beam, the elevation, angle and number of beams corresponding to the geometry of each wing.

Early Group "A" lanterns varied the peak angle (with the angle scribed on the lantern's canopy) whilst Group "AL" lanterns fixed the peak angle at 80°.

Flux emitted from the lower hemisphere of the bulb was uncontrolled, and formed a circular pool of light beneath the lantern. Therefore, the area around the base of the lantern was well illuminated for the pedestrian and house owner (e.g. pavement, front gardens and parked cars) and the road surface was illuminated at longer distances from the lantern for the car driver (e.g. bright road surface, dark kerb edges etc.).

Focusing was variable: the bulb assembly could be adjusted in a vertical axis by moving the tubular bulb holder within the lantern's canopy; a simple locking screw held it in place. The bulb's filament was positioned at the lowest point of the wings for correct focusing, a relatively easy task.




The ESLA Bi-Multi Group "AL" Two-Way 170° In My Collection

facing profile

I obtained this lantern from Croydon where it was being used to light one of the entrances of a private house. Its previous history was not known. Unfortunately the ESLA bracket it was originally installed on had broken and collapsed and was not retained.




front profile

The lantern was in good condition and had been painted white. It had also been remirrored in the past. This remirroring not a perfect job as the rows of mirrors werenít quite aligned properly, but it was worth keeping.




trailing profile

It was stripped and painted silver, which was the colour scheme used by the neighbouring borough of Sutton.




canopy

The lantern's maker and its angular schedule were given on raised letters on raised blocks on the canopy. On one wing:

170°
ESLA BI-MULTI

And on the other it states:

ESLA CANTERBURY
<- PATH   ROAD ->

Unlike other lanterns, it didn't feature the register number or patent number.




pedestrian view

The angular schedule revealed it to be the 170° version. This gave an non-axial asymmetric distribution in plan and would've been used for narrow carriageways (less than 30') with the units staggered.

The "Path Road" mounting instruction on the canopy was required to correctly install the lantern so the main beams were directed over the road..




vertical

Each wing featured the standard ESLA configuration of three rows of cut mirror facets arranged in ten columns.

The lantern has been installed on a ESLA Pole Bracket.




The ESLA Bi-Multi Group "AL" Two-Way 170° As Aquired

This ESLA Bi-Multi was one of two which lit the entrance gates of a large, modern house in Croydon. The lantern was twisted on the bracket so the main beams wouldíve lit the gate, walls and foliage at the front of the house instead of the driveway itself.

The owner looked for similar replacements after this bracket collapsed but when unable to source anything, decided to replace the old brackets with new post top lanterns. She then kindly gave the two old brackets and lanterns to me.

This ESLA Bi-Multi was re-mirrored at some point in the past; the new mirrors do match the facet pattern of the original but donít line up in straight lines. Itís a good enough job so Iíll keep them.

The brackets and lanterns were clearly older than the house but nothing is known of their earlier history. I can only assume they were original Croydon street lights and were purchased as drive lights when removed from service.

The bracket is far too gone to repair (but I do have its sibling) so I'll just salvage the finial, collar and spigot for something else.