We found a very comprehensive and interesting summary Lighting in Museums and Art Galleries by Mr. Alexis Rodriguez Alavarez taken Portal www.archys.com, a site made by students of the Faculty of Architecture at the Universidad Autonoma de Santo Domingo, Dominican Republic. An important element of the study is that the emphasis is on measures to be taken to prevent damage and help the conservation of the works. Then transcribe the document:

I luminación interior, museums and art galleries.

Mr. Alvarez Alexis Rodriguez (Investment Arts)

  Introduction

1 - Selection of sources of light.

2 - Factors affecting the conservation of the works.

3 - factors that define the visual comfort of the facility.

3.1 Quality of light.

3.2 Types of exhibition.

3.3 Environment was created in the work.

3.4 architecture and space.

4 - Economic aspects that relate to the facilities above.

5 - Conclusions

6 - Blibiografía.

Nothing is visible without illumination and lighting too blind and threatens the integrity of the physical world.

Between these two extremes lies the vast room for maneuver illuminator.

In the context of the museum, the room for maneuver is defined according to two major factors: on one hand, the visual quality of the experience sought by the visitor on both cognitive and sensory level, on the other, the need for conservation of objects from the collection.

To make this contrast is properly addressed, it is necessary to take into account a number of factors that determine a project lighting works of art.

1.1        Natural:

It is a light used for years for lighting in museums, with excellent results, for its broad spectrum color and feeling of space offered.

In addition to the above benefits, it is a very cheap light device when its use is to create a scenario of soft light for the works. But it has been wrongly used often used indiscriminately values high and not properly protected.

First, as the daylight a very dynamic, rapid changes in its intensity, orientation, etc.. It is necessary to disseminate and ensure that never falls directly on the site, either through very specific design elements to achieve their integration into the environment or through roofs configurations which meet both requirements. The mix is always advisable to artificial sources, the above aspects.

Second, it must be properly filtered to remove harmful effects such as infrared radiation (IR), its damage by heat and ultraviolet (UV), which affect the photochemical degradation. Moreover, the high values they have, it is often necessary to use screens or blinds to control

There are several ways to introduce natural light into a museum, three of them are:

. Side light is coming primarily from the openings in walls and windows. Is economically cheaper to achieve, however, introduces radiation directly on the work, which increases the deterioration of them and causing the worst effects of glare for high values and angles of incidence.

. Daylight was obtained through skylights or skylights and unlike the previous one, is more costly to obtain the accurate implementation to achieve high levels of waterproofing. Such is the least affected by the dynamic nature of natural light and often achieves the control of radiation directly affect the works.

.   Indirect light: it can be achieved through many options, but basically it is based on the principle of entering the atmosphere for reflection. It is also an expensive option and also needs specialists capable of assessing the conditions, through simulations (in models)   for the effect to be.

1.2       Artificial:

There are two main types of lighting protagonist of art: point and diffuse sources.

      Sources:

Its mission is to wash the surfaces on which you place your artwork.

For this reason, almost pervasive use of the use of tubular and compact fluorescent sources, increasing the use of asymmetric luminaires with optics that allow wider distribution of the works to create homogenous areas along   the whole area.

In several cases, is just what is needed to shed light in others, it requires focus or point sources.

      Point sources.

Their basic function is to create the focus needed to give prominence to the work and incorporate more color values defined for certain objects. It is based primarily on the use of projectors, which can be placed on electrified rails or embedded with incandescent lamps or halogen PAR type of all kinds. Through careful study of the light, positioning projectors extensive radiation combined with intensive, creating an ideal atmosphere to optimally illuminate the details and get a correct perception of the works.

In this type should include the use of fiber optic illuminators with significant advantages:

. Removing the infrared and the possibility of low levels of brightness with no loss of color.

. Possibility of installing light sources outside the windows.

. Easy installation.

. Ease of maintenance, where one source can feed several points of light.

A --   Amount of light or illuminance (E).

The light, as a manifestation of energy in the form of electromagnetic waves, can stimulate or affect vision.

In museums should be considered the exact limits of the amount of light is projected onto the work, not to contribute to the deterioration of them.

The term illuminance specifies the amount of light energy that gets the work and is a parameter that is expressed in lux and is directly proportional to the flux emitted by the light source to the object and inversely proportional to the area is occupied.

There are recommended maximum illuminance values, which have been established by the sensitivity of the work, heat radiation and the display. This must be met for the sources of the artificial daylight.

B -   Duration of exposure to light (T).

The criteria governing the lighting lighting of art galleries, where works are a limited time, are different to those applied in museums, where exposures tend to be permanent.

The effect of damage or deterioration of the work is equal to the level of illumination on the work by the time of exposure to that subject. This means that suffered degradation as a work that is illuminated with 100 lux for 2000 hours, one that is illuminated with 4000 lux for 50 hours.

This aspect, if properly controlled, allowing the speaker, increase lighting levels in some cases, offset by the reduction of exposure to the public or often resort to the rotation of the works exhibited. The following table shows the recommended maximum cumulative values that are accepted in practice to reduce the harm and, in turn, maintain adequate visibility.

Deterioration factor (DF).

Is closely linked to factors that cause damage to a deterioration cumulative and often irreversible, in the works, I mean the infrared and ultraviolet radiation.

Of the two, the most severe are the component of short-wave               

  UV (100 - 400 nm), and that depends on the light source used. The term applies to the artificial daylight.

The potential downside of a light source can be expressed by the so-called deterioration factor. The deterioration factors of lamps suitable for the lighting of museums and art galleries are listed in the table below.

It can be concluded that the deterioration of a work is given by:

Deterioration = E T x x Fd

C -    Composition of the work.

According to chemical   up work will be necessary to implement the above points to prevent the chemical breakdown of materials.

They fall into three broad categories:

Organic materials: usually included in such materials that make up the groups A and B.

Inorganic Materials: including those in group C.

  Composites.

The material damage caused by light can be divided in turn into two main types: thermal and photochemical.

Photochemical effects are attributed to the content of broadcast ultraviolet light source and which depends on its spectral composition. This is the most important effect to eliminate the irreversible damage. The recommended maximum value to be contained light source for museums is 75 m W / lumen.

Ultraviolet light, which is typically 1% of the color spectrum of light sources, said in a rapid deterioration of its effect on the works by the duration of radiation on materials especially sensitive and causes changes in organic materials. The textile dyes and organic dyes lose color paints, varnishes and rioja while binders are darker. Amarillece the role and becomes brittle, so little time in the low-quality material was destroyed.

According to different wavelengths, ultraviolet radiation is classified as:

UV-A (long-wave)                  315-400 nm

UV-B (medium wave)                280-315 nm

UV-C (short-wave)                 100-280 nm

It is now widely practiced filtered light sources that emit high proportions of ultraviolet light to remove high levels of radiation. It is done with filters in different ways: incorporated into the lights, even covering the lamps, or in cases of natural lighting, putting in windows or skylights. If not enough   are added to filter some chemicals to make them more efficient.

The thermal effects are associated with infrared radiation. This aspect is not as bad as the previous one, but the attenuation is also vital.

Infrared light, whose share of the total radiation facilities can reach as high as 90%, thermal damage, combined with the humidity caused by contraction and expansion cracks in the wood painted tables and praise, as well the creation of microorganisms that contribute to the destruction of the works. Some types of suffering from cracks in the glass surface.

Also there is a classification into three types according to its wavelength:

IR-A (short-wave)                  800-1400 nm

IR-B (medium wave)                1400-3000 nm

IR-C (long-wave)                 3000-10000 nm

It is valid to note that the wavelengths of such radiation is commonly expressed in microns or micrometers and not in nanometers. A micron is equal to    1000 nm.

As in the earlier, also applies to use filters to protect the most sensitive. Moreover, with the addition of tungsten incandescent lamps with dichroic reflectors largely reduces the supply of heat over the work but not about the environment, point to be taken into account in calculating climate in the facility. It has introduced the use of optical fibers with a low IR emission of radiation.

The instruments that are used to assess the quantity and quality of lighting available are:

- Luxometro is intended to measure the levels of radiation visible, more specifically illuminance. His unit of measurement is expressed in lux.

- Radiometer is used to measure ultraviolet radiation. His unit is μwatt by the lumen.

- Temperature Probes: used to measure the small rise in temperature. Its unit is the C.

3.1 - Quality of Light

a -   Color temperature:

Is a parameter that is specified in the lamps, which is measured in Kelvin, and refers to the look and tone of light emitted by the light source is, gives a "warm" or "cold" to work . In the case of the paintings, which must be achieved this temperature is as close as possible to that used by the original artist.

b -   Color rendition index (Ra):

Is the parameter on the basis of which the difference between different light sources and considers the nature of their appearance and color saturation of colors, in order to faithfully reproduce the colors of objects. The Ra is measured on a scale of 0 to 100.

c -    Glare.

Parameter is the most complicated and requires a longer time to work, because it should be studied in terms of visual comfort. Manifests itself directly, when the eye sees the light source, or reflected, when the light is reflected on a surface.

Is given for two main aspects:

--        Reflection

--         Contrast

- Reflection:

This comes to cause distraction and in extreme cases forced to change the view of the object displayed.

At the time of placement of the works, one must be careful in the smooth, reflective surfaces or too clear, they are not above the height of the head or take a corner location positioning believe that such effects . Besides illuminating the bodies comply with the positions that are not conducive to the corners or glare   casting sideways. The use of appropriate optical also contributes to the elimination of this effect.

Below is a table with values of reflection of various materials:

- Contrast:

  Occurs primarily over-illumination of the work focused sources that create high levels of illumination in the table with respect to the surrounding environment and create shadow effects that damage the good image of a project.

  We recommend the following stress factors:

Paintings                                      2:1

Three-dimensional objects              5:1

It is valid to clarify that this is a function of a "message" given that it could set the museógrafo. This phenomenon must also be spatially; levels of contrast between the areas of traffic and the exhibition areas can cause side effects in the subconscious of people, leading to cause tiredness or fatigue, which must also be assessed correctly.

We recommend the following stress factors:

Some halls and exhibition areas                   2:1

Among halls and exhibition areas                      3:1

The flexibility of the proposed lighting system contributes greatly to the   elimination of this harmful effect, succeeded in eliminating the harmful impact angles and the use of lighting levels controllers (dimmers), provided that proper placement of work permits for skilled adjustment

d -   Illuminance or light level.

Aspect previously explained.

3.2 - Types of exhibition.

--        Fixed mount.

--        Assembly time.

The first is that which enriches daily and has been developed over the years, reaching needs to increase the factor of retention. The use of optical components, filters to protect the works against harmful radiation, the use of air-conditioning systems with levels of humidity and temperature controlled, limited illuminance values are used to increase resources to the maintenance factor.

The assembly seeks a temporary lighting of the exhibition space as a whole, while contemplating the past. It tends to view the scenic area on the basis of everything that surrounds it, to espectaculizar exposure. In this case, the primary objective of the lighting design is the flexibility in positioning of the points of light.

3.3-Environment which was created in the work.

  This assessment is one of the most complex because it requires a further and deeper understanding of the material to illuminate. It shows that the enormous importance of the merger museógrafo - lighting designer. The works   vary in their conceptions of colors, shades and lighting as time has passed. Each season brings its country and characteristics that differentiate them from the rest.

Become vital in the light under which it was created: to light a candle; daylight, which in turn depends on factors such variables as the intensity that existed at the time or the size of the holes of the windows, the orientation chosen by the artist, time of day light up the atmosphere, which can vary by region within a country.

Anyway, it's a complex issue that is not adequately taken into account on many occasions, but has revived as important as the actual effects chromatic pursued by the painter.

3.4-architecture and space.

Designer lighting installations must be able to face the challenge of serving the interests of both the conservative, who want their collections and items are properly "read" and the architect concerned about space.

This can be even more complicated when it comes to buildings that were designed for other uses and that have a competitive environment with architectural exhibitions.

All of the above   depends on the heights of the ceilings, the presence or absence of windows and skylights, ie the space of the building and the visual design of the architect.

You might need to be built across the lighting for the largest "clean" from the rooftops that the luminaries have no role and are necessary to illuminate a reflection to the placement of space-based systems that give a less personalized architecture.

4-Economics.

At this point, introducing the terms of the energy efficiency of the system and maintenance costs, both initial and operating.

- The effective use of energy is always important in a lighting design. In museums, this helps reduce the consumption of primary energy and environmental pollution exposure. To achieve this it is necessary to achieve a design that uses minimal energy to produce light with the required parameters or spectacular visibility of the facility and operate it for the time it was designed. It is feasible to incorporate automatic controls for lighting levels coupled with the use of natural lighting, use of high-efficiency lamps, lighting fixtures with appropriate optical, high-frequency ballasts, etc.. Finally, the design must consider the need to minimize the levels of illumination to the work of cleaning and security at the facility. - The maintenance work includes cleaning and replacement of defective equipment and lamps.

As the flow of lamps is reduced over time until the time of life, it is important to use, where access is difficult,   lamps of a more appropriate time. This aspect should also apply to windows and skylights that are in the same situation.

Todo lo anterior debe ser previsto por el diseñador de iluminación en conjunto con el equipo de mantenimiento de la instalación responsable de mantener el diseño inicialmente concebido.

- The capital cost of such a facility is considered high, varying depending on the complexity and quality of equipment.

Are also considered high operating costs including energy, maintenance and replacement of equipment and lamps, which could be optimized to satisfy the points outlined above.

5-Conclusions

- Natural light is seen by artists as the light source more appropriate to give justice to the colors and the forms. That is why, after decades, the use of natural light plays a role in museums, art galleries and other venues

- In such projects, when it comes to applying the technique of lighting works of art there is currently no practical methods or rules other than some recommendations given by the ICOM or suggestions that the IES and CIE, Useful to avoid adverse effects in the works

- Whatever the light source is selected, should be protective measures against the factors that degrade and diminish the preservation of books

- Of paramount importance is the proper maintenance and replacement of lamps to ensure the continuity of the initial design criteria, which must be conceived from   a principle and maintained by the staff assigned to these functions.

6-Bibliografia.

- Projects of lighting exhibitions and museums.   IGuzzini.   Italy.

- Lighting for museums and art galleries.   ICSW.   England.

- Guida per l'illuminazione delle opere d'art negli interni.   AIDI    Italy.

- Manual lighting.   Phillips.   Spain.

- L'éclairage dans les institutions museums.   Solotech.   Canada.

- International Review of lighting. Museums 94 / 2.   Phillips.   Spain.

- Restoration and Conservation.    Goethe-Institut.     Germany.

- Museum, Architecture and Museum.     José Linares Ferrera.    Cuba