Shining a light on low-pressure sodium lamps in DESTINY

In the second half of the DESTINY exhibition, a visitor will encounter some floor length, black curtains. Through these, four glass bulbs hang from the ceiling, flooding the room in a yellow glow. Not just any yellow light, but specially sourced bulbs known as low-pressure sodium lamps which emit a virtually monochromatic colour, and results in a flattening or dulling to all other colours.

It was Destiny Deacon’s co-collaborator, Virginia Fraser, who first read about this light source in an art magazine whilst transiting through an overseas airport. Fascinated by the unusual effect it apparently had on colour and the subsequent mood it created in a space, Fraser went about trying to source these bulbs. Due to sodium lamps being disposable items and now obsolete technology, not an easy task! However once found, Fraser and Deacon together developed an art installation titled Colour Blinded which utilised their full impact.

The colour-draining or neutralising effect of this light pairs beautifully with some of the many themes running through Deacon’s exhibition: skin-colour discrimination and racism. Indeed, human skin tones become indiscernible, rendering only in various shades of grey.

Low-pressure sodium lamps (LPS), also known as SOI or SOX lamps (SO for sodium)ii, were first invented in 1920 by Arthur H Compton for Westinghouse, in Pittsburgh, USA. The problem with the early models was that the highly corrosive sodium would degrade and blacken the housing made of regular silica glass. Advancements were made by Marcello Pirani at Osram in Germany when he invented a sodium-resistant glass in 1931. Commercial production of LPS lamps began in 1932 by Philips in the Netherlands.¹Sodium Lamp, High lumen output at high efficiency (1920-Today) >> edisontechcenter.org/SodiumLamps (accessed 08.08.2020)

Bulbs were manufactured from an inner glass ‘discharge’ tube containing solid sodium, neon and argon gas, surrounded by a secondary glass vacuum chamber which offered thermal insulation. When the inner tube is initially lit, a pink light warms the sodium metal causing it to slowly vaporize. Within 5-10 minutes, the emission becomes the characteristic strong yellow with spectral lines at 589.0 and 589.6 nm. When objects are illuminated by this extremely narrow bandwidth, colours are very difficult to distinguish.²Sodium-vapor lamp en.wikipedia.org/wiki/Sodium-vapor_lamp (accessed 08.08.2020)

LPS lamps are extremely efficient, largely due to them using all their current to create a light in this narrow bandwidth which is close to the peak sensitivity of the human eye. Modern versions have a service life of approximately 18,000 hours and lumen output does not decline with age, although energy consumption does increase. They provided low-cost solutions for illuminating large outdoor areas and were primarily used as streetlights and for security lighting. LPS lamps have also been a preferred light source where light pollution is a concern such as near astronomical observatories and wildlife nesting sanctuaries.²Sodium-vapor lamp en.wikipedia.org/wiki/Sodium-vapor_lamp (accessed 08.08.2020)

Considered an improvement to LPS lamps, high-pressure sodium lights (HPS) were first developed in 1955 by the General Electric Research Lab in New York and Ohio, USA and put into production in 1964.i As the name suggests, the inner tube is under higher pressure and contains a mixture of metals producing a broader range of light wavelengths. Their improved colour rendition, still yellow/orange yet with a white component due to the presence of mercury, came at a slight cost of efficiency compared to their predecessors.³Lighting Comparison: LED vs High Pressure Sodium (HPS) and Low Pressure Sodium (LPS) stouchlighting.com/blog/led-vs-hps-lps-high-and-low-pressure-sodium (accessed 11.08.2020) Still, HPS lamps became the most popular street lighting source world-wide for many years before slowly being replaced by other metal halide lights and more recently fixtures with light emitting diodes (LED’s). HPS lamps are still used today for some economical outdoor lighting applications, and in horticulture to assist in plant growth.³Lighting Comparison: LED vs High Pressure Sodium (HPS) and Low Pressure Sodium (LPS) stouchlighting.com/blog/led-vs-hps-lps-high-and-low-pressure-sodium (accessed 11.08.2020)

Philips Lighting, the last manufacturer, ceased production of LPS lamps in November 2019 due to failing demand.²Sodium-vapor lamp en.wikipedia.org/wiki/Sodium-vapor_lamp (accessed 08.08.2020)

Fraser and Deacon loaned the NGV four LPS bulbs and related equipment for the DESTINY exhibition. NGV electricians tagged and tested the accompanying cords and electrical transformers and mounted the latter in the ceiling of the exhibition space. Without any LPS lamps in reserve in case of failure during the exhibition period, conservators began an online search to find identical bulbs. This proved to be more difficult than expected and all attempts to source within Australia were futile. Six were eventually located from a supplier in the UK, General Lamps Limited, purchased and shipped to Melbourne. Unfortunately, two lamps broke in transit. The remaining four are now being carefully stored, yet are within easy access, if required during our DESTINY show.

Furthermore, they offer peace of mind knowing the NGV can re-create this unique experience for Deacon and Fraser displays into the future.

Janelle Borig is Conservator, Exhibitions and Loans, National Gallery of Victoria

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