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Thankyou to Bob Child, Head of Conservation, National Museum Wales for the content below.
Please note that this content is presently only available in English. We hope to have a Welsh version as soon as possible. We apologise for any inconvenience.
Lighting in Museums : The new choices
Increasingly we are being encouraged to use lighting that is more efficient, economic and ecologically friendly. It is often pointed out that a standard 100W tungsten bulb produces only about 5W of light - the rest is wasted heat, and the bulbs will typically only last 1000 hours before needing to be replaced. Low wattage, long life, mini fluorescent replacements are often lauded as being ‘better’ despite the fact they are more expensive to produce, give light that is not universally liked and contains mercury, giving toxic disposal problems.
New lighting systems have been introduced, including tungsten-halogen low voltage lights, mini fluorescent bulbs and recently, light emitting diodes (LED). Some of the new energy-saving bulbs are compatible with older fittings, especially on 240v systems, but manufacturers should be consulted with low voltage tracking etc. Faced with the choice of lights for new exhibitions or retro-fitting older galleries, what decisions should be made?
Good quality museum lighting should satisfy the following criteria:
However, this is only part of the story. We also need to think of many other aspects of museum quality lighting. Some of these are aesthetic considerations in viewing works of art, others are conservation aspects on the damage that the light can cause.
Light, as we see it, has many properties. It has colour, so that candlelight and tungsten bulbs have a yellowish colour while northlight daylight and cheap fluorescent tubes give out a blueish light. This can be quantified as a colour temperature which is the temperature measured (in Kelvin) of a black metal heated up until it glows with the same colour as the light source. Typically, colour temperatures are:
Candle 1900K yellowish - ‘warm’
100W tungsten bulb 2900K
20 W tungsten-halogen bulb 3100K white -
Noon daylight 5000K blueish - ‘cold’
‘Warm’ lighting is more comfortable at low light levels, and is to be preferred in museum lighting of vulnerable material.
Daylight tungsten bulbs and tungsten halogen bulbs give perfect colour rendering, as they contain the full colour spectrum. But fluorescent tubes, LED lights and discharge lighting systems make light in a different way and may not have a full colour spectrum and therefore not show colours truly. Their colour ability is measured by a scale called the Colour Rendering Index (CRI). For most museum situations, a CRI of 90+ is suitable for viewing coloured objects.
Mini fluorescent replacement lamps have a CRI of about 76
Tungsten-halogen lamps have a CRI of 99
LED lights are increasingly improving their CRI and commonly
Have a RI greater than 80
In terms of economy, cold cathode and LED lights are very efficient and have very long usage life. Typically, they come as 3 and 4W, which is equivalent to a 20w tungsten-halogen bulb, and lasting in excess of 40,000 hours.
In general, it makes sense to change to LED lighting where possible for economy of use in electrical costs, but also in reduced maintenance. The fittings and bulbs are initially quite expensive. Normal warm-white or cool white bulbs with a CRI over 80 are generally acceptable, except where very accurate colour rendition is essential.
For further information on fittings, lamps etc. go to www.initiallights.co.uk <http://www.initiallights.co.uk>.
They can often be direct replacement bulbs in 240v systems, but specialist advice is needed if replacing bulbs in low voltage systems.
R.E. Child
Head of Conservation
National Museum Wales
Current Awareness Service
Inclusion of third party information in the Museums Current Awareness Service does not constitute an endorsement by CyMAL. CyMAL takes no responsibility for the quality of third party events, products or services featured in this Newsletter. Whilst every care is taken to provide accurate information, neither CyMAL nor the editor undertakes any liability for any error or omission.
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Welsh and English versions of the bulletin will remain separate in response to requests from readers.
Carol Whittaker AMA
Museums Development Adviser
CyMAL: Museums Archives and Libraries Wales
Welsh Assembly Government
01970 610 238
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