UV Filters

UV Filters  Pegasus Associates Lighting has several UV filters including Optivex glass UV filters and UV filtering tube guards that can be used to protect valuable items against photochemical degradation.

Pegasus Associates Lighting has several UV filters that are perfect for retarding photochemical degradation in a variety of sensitive materials like textiles, historical documents, and works of art. These UV filters are intended for use in museums, art galleries, libraries, and other areas where the prevention of ultraviolet (UV) light degradation is critical.

Valuable UV Filter Information

Optivex Glass UV Filters		SoLux MR16 Lamps with UV Filters
	Eliminates 99%+ UV radiation Limits photochemical degradation Several sizes & shapes Starts at $18.30 Learn more		VERY low UV CRI of 98+ 4 Beam spreads $10.50 /lamp Learn more
T8 UV Filtering Tube Guards		T5 Clear UV Filtering Tube Guards
	0% transmittance below 395nm T8 lamps Four feet long or shorter $122.90 per case of 24 Learn more		0% transmittance below 395nm T5 lamps Four feet long or shorter $179.90 per case of 24 Learn more
T8 Amber UV Filtering Tube Guards
	0% transmittance below 540nm T8 lamps Four feet long or shorter $306.00 per case of 24 Learn more

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VALUABLE UV FILTER INFORMATION

Ultraviolet Radiation | Measurement of UV Radiation | Photochemical Damage

Reciprocity Law | Types of UV Filters | How to Reduce UV Damage

Ultraviolet Radiation

Ultraviolet (UV) radiation is invisible to the naked human eye and is generally considered to be that radiation which has a wavelength of less than 400 nanometers (nm) and greater than 100 nm.

Ultraviolet radiation is part of the electromagnetic spectrum between visible light (which is above 400 nm) and X rays (which are below 100 nm). Ultraviolet radiation is divided into three bands: UVA (315-400 nanometers), UVB (280-315 nanometers), stronger radiation that is the common cause of sunburn; and UVC (280-100 nanometers), the strongest and potentially most harmful form which is used to sterilize surfaces because it kills bacteria and viruses.

Virtually all light sources emit some amount of UV radiation along with their visible emissions. Some more than others. For example, there is a much higher proportion of UV energy in daylight radiation (natural sunlight) through glass than in incandescent, halogen, or fluorescent light sources shining through glass. When comparing artificial light sources HID light bulbs (high intensity discharge lamps) probably emit the most UV radiation, fluorescent light bulbs would be next, then tungsten halogen lamps, then standard incandescent light bulbs.

Measurement of UV Radiation

The typical light meter used to measure illuminance in foot-candles (fc) will NOT give a good indication of the amount of UV radiation that is present.

A standard device that measures UV radiation is the Crawford UV Monitor manufactured by the Littlemore Scientific Engineering Co. in Oxford, England.

UV radiation is measured in microwatts of UV radiation per lumen (µW/lm). This is useful for checking a particular lamp or window because the proportion of UV radiation does not change with the distance from the light source.

Traditionally, conservators have recommended that if a museum light source emits more than 75 µW/lm of ultraviolet radiation, it requires a UV absorbing filter. Recently, new recommendations by the staff at the Canadian Conservation Institute suggests eliminating UV radiation completely, aiming for under 10 µW/lm through the use of window films, UV absorbing light covers, and UV absorbing filters.

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Photochemical Damage

Fabrics and paper become brittle, fade in color, or turn yellow when exposed to sunlight. A good example is that of street maps or magazines left in a car below the rear window. Printed paper articles left there often change noticeably within a few weeks. Those changes are mainly due to exposure to the UV radiation in sunlight.

Natural high polymers from cellulose and protein are decomposed by solar radiation with a high percentage of UV light. Cellulose fibers, from which paper is made, are particularly sensitive to UV radiation. In conjunction with water, which is always present in the fibers, and under UV rays, atmospheric oxygen reacts with the water to form hydrogen peroxide. This results in a gradual oxidative breakdown of the cellulose. This breakdown is the main factor causing decomposition of cellulose in light. Consequently, because oxygen and moisture cannot be eliminated, every precaution has to be taken to prevent the exposure of valuable articles of paper or cellulose fiber to UV radiation. Similar reactions can be seen in some pigments causing colors to fade.

Photochemical damage (damage due to chemical change by radiation) of a fabric or a painting is related to the wavelength of the radiation striking it. Ultraviolet (UV) radiation causes more damage than the same amount of visible blue radiation, which causes more damage than the same amount of visible yellow radiation, which causes more damage than the same amount of visible red radiation. If a “Probable Relative Damage” (PRD) factor is assigned for different wavelengths, the shortest UV rays would rank highest and the factor would decrease exponentially with increasing wavelength. For example, the PRD factor for UV light of 300 nm would be approximately eight, for UV light of 380 nm, one, and for visible green light of 500 nm, .03. This illustrates the importance of filtering out UV light to protect valuable materials.

Photochemical damage can occur in organic materials, textiles, watercolors, paper, oil paintings, leather, and glue just to name a few.

Both UV and visible radiation can cause color change and surface deterioration. Therefore, it is not sufficient to remove only the UV radiation; it is also very important to minimize visible radiation.

Damage from light is cumulative and permanent; its effect on artifacts cannot be reversed by subsequent storage in darkness.

Reciprocity Law

In general the same amount of photochemical damage will be produced by a strong light in a short time or a weak light in a long time. If illuminance is measured in foot-candles (fc) and the time in hours, 10 fc on a painting for 5 hours gives it an exposure of 50 foot-candles-hours and 5 fc for 10 hours would give it the same exposure. In reducing damage by light the most effective strategy is clearly to reduce both illuminance and the time of exposure.

Note that the Reciprocity Law does not state that twice the exposure will cause twice the amount of fading. Rates of fading commonly decrease with time, until there comes a point when no more fadeable material is left.

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Types of UV Filters

Pegasus Associates Lighting presently offers three methods of reducing the amount of UV radiation: Optivex® glass UV filters, UV absorbing plastic tube guards for linear fluorescent light bulbs, and SoLux® MR16 light bulbs with UV filters. UV absorbing prismatic plastic diffusers for light fixtures and UV absorbing, clear, plastic film are two materials that we do not now offer.

Optivex® Glass UV Filters are an excellent way to reduce UV radiation by eliminating virtually all UV radiation (over 99%). These UV filters come in various circular sizes and can also be purchased as a rectangular sheet with dimensions up to 10in by 30in.

SoLux® MR16 Light Bulbs with UV Filters have the lowest UV output of any low voltage MR16 lamp (8.55 µw/lm). These lamps come in four different beam spreads (10°, 17°, 24°, & 36°), three different color temperatures (3500K, 4100K, & 4700K), two different wattages (35W, 50W), a very high color rendering index, and have reduced infrared (IR) radiation as well (76% less than standard MR16 lamps).

UV Filtering Plastic Tube Guards  Please note that the terms, “UV absorbing”, “UV filtering”, and “UV inhibiting” are all, more or less, synonymous. These terms, however, are quite different from the term, “UV stabilized”. This latter term simply means that the plastic used to made the tube guard is resistant to photochemical degradation. UV filtering tube guards are of relatively high permanence and can be expected to last at least ten years. These tube guards generally block UV radiation up to about 395 nm.

UV filtering acrylic diffusers and lenses can be made for light fixtures from specially formulated UV absorbing (UVA) acrylic. The diffusers can be made of clear, prismatic acrylic and can be made to “wrap around” light fixtures to replace the wrap-around diffusers that are now there. Flat clear lenses made of these prismatic acrylic sheets can be cut to almost any size to replace the lenses of various recessed fluorescent light fixtures (commonly called troffers). This unique UV filtering acrylic material is specifically created for use in museums, art galleries, libraries and other areas where UV degradation must be reduced. Ordinary acrylic will block out UV radiation with a wavelength of less than about 350nm while the special UV absorbing (UVA) acrylic can block out UV radiation with a wavelength of less than about 390nm — a significant improvement.

UV filtering plastic sheeting film filters out 98% of the UV radiation below 400nm. It is often used by museums, art galleries, libraries, and private collectors for picture framing and display cases. This same special clear, flat, acrylic also comes with a matte finish which minimizes glare and an abrasive-resistant finish which minimizes minor scratching caused by commercial cleaners.

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How To Reduce UV Damage

To minimize photochemical degradation the amount of natural illumination (sunlight) must be minimized if not eliminated altogether.

To minimize photochemical degradation the amount of artificial illumination (from fluorescent, incandescent, and halogen light sources) should be minimized to no more than what is necessary for proper viewing and the time of illumination should be minimized as much as possible.

To those who are viewing the exhibit the quantity of light in an exhibition space seems to be less important than the balance of illumination levels between the works and the remaining space. In general, 10-25 fc of illumination is probably adequate for the perception of detail in the works of art being shown. Remember, good viewing of exhibits is not determined solely by the amount of light incident upon the piece. Other factors play a role as well — especially the amount of glare present. Visible light levels should be kept at a minimum. Usually 5 fc is recommended for watercolors and textiles; 15 fc is recommended for oil paintings, wood, and leather.

Use UV filtering materials such as Optivex® glass UV filters, UV filtering tube guards, SoLux® MR16 light bulbs with UV filters, UV filtering, prismatic, acrylic light fixture diffusers, and/or UV filtering plastic film. It is essential to re-check the adequacy of these filters (especially the plastic filters) periodically since they often deteriorate over a period of years.

White paint that contains titanium dioxide is a fairly good absorber of UV radiation. Therefore, white paint might be used to control the amount of UV radiation in a given space.

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Optivex Glass UV Filters | SoLux Daylight MR16 Lamps with UV Filters

Clear T8 UV Filtering Tube Guards | Clear T5 UV Filtering Tube Guards | Amber T8 UV Filtering Tube Guards

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