Illuminati Creative Technology, Colchester UK

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Stage Lighting: A basic technology manual.

Conservation Lighting for Museums and Galleries

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are there to provide an environment where precious and interesting objects can be conserved, preserved and made available for the public and scholars to see.

It is of the essence that they be presented in such a way that the original colours and forms are clearly shown.

 However, modern presentation  vernacular tends toward an interpretive approach: This can mean for example that the object be shown in a context which may include projected images,  and modeled with several light sources.

Where old or precious objects are involved, this spells ..............


The amount of damage depends on six thing
1) The luminous energy contained in the light.
2) The thermal energy contained in the light.
3) The material of the target surface.
4) The condition of the target surface.
5) The reflectivity of the target surface.
6) The length of time the light falls on the target.

The damage can consist of:
1) Fading (Photochemical Degradation of the surface).
2) Degradation and cracking of paint and bindings (Heat damage caused by continuous heating)
3) Buckling, loss of adhesion and chemical changes  caused by alternate heating and cooling.
4) Encouragement of bacterial and fungal growths.

Indirect heat produced by light sources can normally be controlled by the use of proper environmental control measures including  air conditioning and humidity control, etc., provided that the fittings can be placed at a reasonable distance from the exhibit and not in a confined space within the exhibition case.
However the radiant heat produced by a tungsten or tungsten halogen lamp can be quite considerable is important, however that the direct heat from the beam of a spotlight must be removed as far as possible by the use of dichroic lamps and / or heat filters.

Damage to art works is caused partly by visible light, but mainly


What is UV?
In the visible portion of the spectrum, the various colors perceived by the human eye correspond to wavelengths ranging from about 0.0004mm  (400 nanometers) (Violet), to about 0.0007 mm.(700nm) (Red).  The various colors of the spectrum fall between these limits.

The colour component of this segment of the spectrum may be seen when a narrow beam of sunlight is passed through a glass prism to form a band of colors that extends from red at the long wavelength end to violet at the short wavelength end.  The radiation dispersed by the prism actually extends farther in both directions. Beyond violet lies Ultra Violet. This behaves in every way like visible light, but cannot be directly perceived by the human eye.

Ultraviolet light is generally divided into:
1)  the near UV regions (350-380nm), used for the excitation of fluorescent materials,

2) The Far  (200-300 nm.) regions. Sun lamps, consisting of a fluorescent tube and a mercury vapor lamp, produce a spectrum of radiation that is similar to that of the Sun. It should be used with caution.  Sunlight, both artificial and natural, damages the skin and can cause cancer.  The strong ultraviolet component in sun lamps also makes irritation of the eyes and cataracts a serious risk, and eye protection should be worn to filter out the harmful bands.   Far ultraviolet light has the ability to destroy certain kinds of bacteria, and is used for sterilizing foodstuffs and medicinal equipment.

3) the vacuum (200 to 4 nm,) ultraviolet regions. The last wavelengths, which are particularly harmful to life, are strongly absorbed by the Earth's atmosphere and particularly by the OZONE LAYER.

Ultraviolet light is created by the same processes that generate visible light--transitions in atoms in which an electron in a high-energy state returns to a less energetic state.

 Fluorescent and mercury-vapor lamps produce large amounts of ultraviolet light, which is filtered out when the lamps are intended for optical use.  Visible light may instead be filtered out to achieve black-light effects, through the induced luminescence of objects by ultraviolet light.

Biological effects of ultraviolet light include sunburn and tanning.  Excessive exposure has been linked to the development of skin cancers and of cataracts in the eye.  Far ultraviolet light, which has the ability to destroy certain kinds of bacteria, is used for sterilizing foodstuffs and medicinal equipment. A sunlamp, consisting of a fluorescent tube and a mercury vapor lamp, produces a spectrum of radiation that is similar to that of the Sun.  As a result, even though a sunlamp can be used for therapeutic purposes or for artificially inducing a skin tan, it should be used with caution.  Sunlight, both artificial and natural, damages the skin and can cause cancer.  The strong ultraviolet component in sunlamps also makes irritation of the eyes a serious risk, and eye protection should be worn to filter out the harmful bands.

 Ultraviolet light fluorescence can reveal changes in the surface, repairs, fills, the presence of a varnish film, recent retouches, and the presence of certain pigments, resins, waxes, and minerals. Paper, photographs, parchment, leather, and textiles are extremely sensitive to excessive moisture and are susceptible to fungus attack.  Exposure to sunlight may cause immediate fading of watercolors, textiles, and wallpaper.  One day of 90 percent relative humidity may cause corrosion in polished metals, which would be aggravated by the presence of any polish residue.  Variations in humidity cause warping and checking of wood, especially in large objects and veneered furniture. Ivory, drizzled glass, salt-infused archaeological pottery, and painted, gilded, and gessoed wood all react unfavorably to moisture, which may be further catalyzed by heat, light, and atmospheric pollutants.  The museum conservator must supervise the maintenance of stable environmental control as well as provide first aid or complete restoration of damaged or deteriorated artworks.

Minimizing damage to artworks

Photons of light can bit by bit destroy organic materials such as paper, textiles, inc, dyes, carbon etc by , so it is of the essence to reduce the total number of photons that hit the work to the absolute minimum required for the accurate rendition of the colours and shapes. There is a "slide rule" that trades-off light levels against time of exposure, but in general the total exposures given below should not be exceeded for an eight hour day. Other methods include automatic systems that turn the lights off when not required, using occupancy detectors, pressure mats, automatic blinds etc.

1) Works of art on paper and very sensitive materials, such as prints, drawings, watercolors, dyed fabrics, manuscripts, and botanical specimens Light must be kept to less than 50 lux (5-10 foot candles) for no more than five hours a day. Cabinets containing very valuable and delicate drawings should be fitted with heavy blinds where natural light is present.
2) Works such as Oil paintings, watercolours most photographs, ivory, wood and lacquer objects and sculptures containing or finished with organic materials such as resins, waxes, paints : 150 lux or up to 15 foot candles
3) Sculptures of metal, stone, bronze etc: These are thought to be unaffected by strong light. However, remember that heat can also do damage.

Sources of Light

1) Natural light: By far the largest source of light in the Gallery or museum is from natural sunlight. A good natural north light is often specified by art gallery curators as it can give an even coverage and  good colour rendering, especially if it is well diffused with scrim, and supplemented with the right amount of high colour temperature fluorescent tubes, on an automatic light level detection system. Normal glass windows do not filter out sufficient UV in the near band to be effective, and UV levels can be far too high for far too long in the summer months. Special toughened laminated UV blocker glass for glazing purposes is available in sheets 8mm thick up to 2.2m x 1.5m. This claims to reduce UV in the 300 -400 nanometer range to ‘less than one per cent’. Heavy acrylic sheet can be effective up to a point.

2) Fluorescent tubes, 'energy saving' compact fluorescent lamps and discharge lamps: These give quite a lot of UV and should be avoided unless heavily filtered

3) Incandescent lamps, reflector spot lamps, par lamps, theatrical profile and fresnel fittings: These give somewhat less UV than other types, but can still cause heat and photon damage. There is a  filter by GAM Colour No 1510 called UV Shield which filters UV in the range 300 -360 to virtually zero, but will allow UV between 360-400 at up to 20%. Visible light is attenuated by about 10%.

4) LED and Fibre Optic sources. These give virtually zero UV, and are highly controllable.

The following is reprinted from a technical note by the Exhibition Alliance

Measuring Light Intensity
With a Footcandle Meter or a Lux Meter:
Light meters that convert the reading directly to footcandles or lux can be ordered. They
will measure either the light from the source (incident light) or the light reflected from the object. Follow the manufacturer's instructions.

With a camera light meter:  The method recommended by the Canadian Conservation Institute measures reflected light. It requires a 35mm single lens reflex camera with a built-in light meter, and a white card measuring 12" by 16".
1. Set the camera film-speed reading at 800 ASA, and set the shutter speed at 1/60 of a second.
2. Have someone hold the white card in front of the art work and at the same angle as the art work.
3. Position the camera so that the card just fills the view screen.
4. Adjust the aperture setting until the camera's f4 indicates 50 lux or 4.6 footcandles
f5.6 indicates100 lux or 9.3 footcandles,
f8 indicates 200 lux or 18.6 foot candles,
f11 indicates 400 lux or 37.2 foot candles,
The results of this method are not as accurate as those of a lux or footcandle meter, but we found them to be within 3 foot candles of the footcandle meter reading.

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