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T2 Lamps – Less is more

The text below was that submitted to Museum Practice Magazine for their article ‘T2 lamps – less is more’. It was published in Museum Practice, issue 10, spring 1999.

T2 lamps – the magic wand for lighting?

The relatively new T2 lamp is a pencil thin fluorescent lamp that can have a number of uses in museum lighting. Its slim shape means that even with a reflector and body around it the final luminaire can be as small as 25 by 25mm, making it ideal for fitting into tight corners.

The lamp is available in 6, 8, 11 and 13W versions which are about 220, 320, 420 and 525mm in length. The range of lengths and outputs mean that they can be easily grouped to fit into many different shaped spaces. They have a higher output & greater efficacy than older, wider 6W to 13w T5 lamps whilst having similar lengths.

The lamps are available with colour appearances from warm to very cool (3000K, 3500K, 4000K and 6000K) and the colour rendering index is 85 which puts it into the ‘very good’ quality category 1B. This colour rendering is acceptable for most museum and gallery use. However, as the CIBSE ‘Museum and Gallery’ lighting guide points out, there are certain materials that do not respond well to the non-continuous spectrum of fluorescent light.

Due to the exacting electrical characteristics of these lamps they have to be operated from a dedicated electronic ballast. This ensures both efficient operation and a simple, safe shutoff at the end of life. So there is no annoying flickering and fading. Luckily this control gear has also been made slimmer than conventional gear being only 280 mm long and 32 mm by 16 mm in cross section. So again concealment is again relatively easy.

The narrow diameter makes these lamps ideal for putting some good optics around them. It is easy to get a reflector that will produce a very narrow beam, or should we say sheet, of light. Alternately a different louvre can produce a good asymmetric throw that can be used for lighting across a flat object such as a poster or wall panel.

Whilst these lamps and their luminaires make them ideal for using within showcases they still produce heat that may affect objects within the case and will still need access for re-lamping. In addition the UV output is slightly higher than other similar output fluorescent lamps which exceed the CIBSE conservation limits. For these reasons they can be used in shop cases and cases exhibiting non-delicate objects quite freely, but great care should be taken with these, and indeed any other lamps system, if use in within the ‘secure’ part of a general exhibition case is intended.

One small future complication to note is the lighting industry’s long term intention to alter its designation of fluorescent lamp sizes from the present imperial system to the metric one. The old British ‘T’ system referred to eighths of an inch, in other words a T2 lamp would be two eighths of an inch in diameter. The new metric system refers to millimetres. So the lamp discussed above, being about 7mm in diameter, would be called referred to in literature as a T7 lamp. Similarly the old British T8 lamp would become a European T25 lamp!

References:

CIBSE Lighting Guide 8, ‘Lighting for museum and art galleries’. 1994 (CIBSE – tel. 020 8675 5211)

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