Care For Your Philatelic Stamp Collections
(UV light and its harmful effects on your items of Philately)
For sensitive materials (19th and early 20th century stamps), an accepted level of ultraviolet (UV) light is .375 uw/cm2 (micro watts per square centimeter). Compare this figure to that of typical room illumination, direct sunlight, and UV authentication lamps, which can produce respective levels of ultraviolet light on the order of 6 uw/cm2, 6000 uw/cm2, and 20,000 uw/cm2!
As with VISIBLE light, the effects of ultraviolet (UV) light are cumulative and irreversible, and overexposure will eventually cause the "light bucket" of your philatelic collection to overflow, for example, as by decomposition of inks, pigments, papers, plastics, and gums. As evidenced by the discolored, faded, and oxidized appearance of the plastics and papers used with many of our philatelic collections, overexposure to ultra violet light can also cause other types of direct or indirect damage. Because UV wavelengths of light do not help to make your stamp collection any more visible for viewing, their elimination or minimization should be considered to be a win-win situation.
Although ultra violet UV light spans the wavelengths of 260 to 400 nanometers (nm), the shorter 260-320 nm UVB wavelengths are mostly blocked by the ozone layer, by window glass, and are not emitted by typical home/office lighting. For this reason, elimination of UVA wavelengths of light is where efforts at minimization and elimination are normally directed.
UV resistant plastics and glass ... are they safe to use with items of philately?
An observation is now made with regard to use of plastic holders, sleeves, and other storage and display materials. With regard to the plastic holders and sleeves used for display of stamp and philatelic items, many manufactures of these philatelic products like to tout their protective resistance to ultra violet light, however, what they typically fail to mention is that even if the plastic itself may be of the "inert" archive grade PET (Mylar®) polyester type (see Effects of Plastics), the coatings and compounds used to make their products ultra-violet UV resistant are not. If it is anticipated that UV resistant archival PET type plastics will be in physical contact or close proximity to items of particular aesthetics, history, or value, it should be only for limited periods of time, otherwise one evil (ultra-violet light) may end up being eliminated and replaced by another (the decomposing chemicals used to make the plastics UV resistant).
Effects of ultra-violet light on philatelic and stamps in home/office environment
One particular UV light figure of merit that should be of interest to stamp collectors is that of .375 uw/cm2, which is accepted by many museums as the maximum level of ultraviolet light that should be present in a 50 lux VISIBLE light environment. Note: 50 lux is the maximum amount of VISIBLE light that is recommended for viewing and displaying of 19th and early 20th century philatelic and stamp items.
The units of uw/cm2 are used to measure ultra-violet UV light and are relatively easy to understand (i.e. amount of power distributed over a given area), however, many museums prefer to measure ultra-violet light with specialized sensors that make UV measurements in units of microwatts per lumen (uw/lm); unfortunately these units are intuitively a little bit more difficult to understand. The units of uw/lm units represent the amount of ultra-violet UV light present in a given amount of VISIBLE light, where lumen is a measure of the quantity of light emitted by a source, and 1 lumen spread over 1 square meter is equivalent to about 1700 lux. For reference, a 100 watt incandescent bulb emits on the order of about 1700 lumen. Unlike measurements made in the units of uw/cm2, measurements made in uw/lm remain constant regardless the distance from a particular UV light source the measurement is taken.
|VISIBLE Light Condition
||Typical UV power measured in uw/cm2
||Typical UV power present as a percent of VISIBLE Light
|Direct Bright Sunlight
|300 lux in office/home with fluorescent lighting
|Office with low UV Fluorescent lighting
||.5 - 2 uw/cm2
|100 lux from 100 watt bulb at a distance of 3 ft
|Museum Lighting at 50 lux (19th and early 20th century stamps)
|100 Watt UV Authentication Lamp measured at 2 inches
||No VISIBLE light present
|100 Watt UV Authentication Lamp measured at 10 inches
||No VISIBLE light present
The table to the left is a collation of UV light measurements that were made under different VISIBLE light levels. The recommended amount of VISIBLE and UV light for 19th and early 20th century stamps is indicated in blue. In a museum, a typical level of UV light that is acceptable is about 75 uw/lm. In units of uw/cm2, this same level is about .375 uw/cm2. At first glance, the 75 uw/lm level of UV light found in a typical home/office may appear to match the accepted 75 uw/lm of UV light in a museum setting, however, the two measurements are actually quite different when compared in units of uw/cm2. The reason is this: because the units uw/lm represent the amount of UV light present in a given amount of VISIBLE light, and because there is much more VISIBLE light in an office (300-500 lux) than in a typical museum environment (a 50 lux environment), 75 uw/lm in a 300 lux office represents a much larger proportion of UV light than is present in a museum. How much more can be understood by comparing the .375 uw/cm2 level found in museums to the 6 uw/cm2 level of UV light found in a home/office, which is about 16 times more UV light than is acceptable. As discussed shortly, this level can be relatively easily reduced to more acceptable levels.
The measurements presented in the table above were collated from a number of sources that were not all in absolute agreement. Other than the UV values given for the 50 lux condition museum level of VISIBLE lighting, the other values are given only for an indication of relative differences, not absolute values, which because of variances in measurement conditions and measurement instruments can vary by orders of magnitude.
For typical indoor home/office setting, many easy to implement techniques can be employed to reduce UV light to the museum accepted level of .375 uw/cm2. These philatelic protection techniques include simple steps such as using shades over window glass, low UV fluorescent lighting, and ultra-violet filters placed over window and light fixtures. However, because the amount of ultra-violet UV light present in VISIBLE light is more or less proportional to VISIBLE light, the most simple protection technique of all is that of turning down the lights (for example to a 50 lux level). These philatelic protection techniques alone, or in combination, can all but eliminate the types of harm damage that UV light is capable of.
Despite any desire you may have to reduce ultra-violet UV light in your home/office settings, it should not be forgotten that your primary goal should be to reduce the level of VISIBLE light. Although, UV light overexposure is harmful, at the relatively low levels present in typical homes and offices (even without UV filtering), any cumulative effect UV light may have on the "light bucket" can easily be overshadowed by the effects of overexposure to VISIBLE light (see Effects of Visible Light). On the other hand, exposure to UV light from UV authentication lamps should be considered in an entirely different context.
Thinking of authentication of your philatelic items via use of UV light ... consider the following before doing so!
The amount of ultra-violet UV light that a typical 100 watt UVA wavelength authentication lamp (of the type shown below) produces can be as much as 20000 uw/cm2. Depending on the type of lamp used, this is up to 60,000 times! the amount of UV light allowed in a 50 lux museum environment.
It should be remembered that even if ultra-violet UV authentication lamps are used intermittently, their effects will be no less cumulative than that of VISIBLE light. Consider the following hypothetical but very possible scenario: what if over the last 100 years 10 different owners of the same philatelic item determined that before their purchase they needed to determine its authenticity? What if each of the 10 owners allowed authentication by UVA light (of the type shown to the right) for a period of 30 minutes? Assuming this to be the case, the philatelic item would have been exposed to a cumulative (10 x .5 hour x 20,000 uw/cm2) = 100,000 uw/cm2 of ultra-violet light. Compare this to an item of philately exposed to UV light under 50 lux in a museum, which would (with 8 hours a day exposure over the last 100 years) have been exposed to 100 x 365 x 8 x .375 uw/cm2 = 109,500 uw/cm2 of UV light. Note: our 100,000 uw/cm2 calculation does not take into account that at the high UV power levels of a UV lamp, disproportionately more damage is caused than at lower power levels, or that authentication would probably also have been made under the shorter more damaging UV wavelengths of a UVB lamp. Thus, if authentication of your stamp has occurred as above, there is a very good chance that if the UV "light bucket" of your philatelic item has not been filled yet, it is very close to being so.
Once authenticated under UV light, how many times do our philatelic treasures need to be subjected to the process again?
We posit this final question for consideration by philatelists, stamp collectors, auction houses, and authentication services alike: once authenticated under high intensity ultra-violet UV light, should there be some responsibility taken to minimize future exposures to the high levels of UV lamps (note: we do not imply re-grading of an item of philately should occur only once, however, when it is so done, can it be without unneeded repeated exposures to UV lamps)? Except in the exceptional cases of newly discovered fraud or forgery, once a philatelic item is authenticated by a respected authority, what justification can be made to authenticate the same item over and over under UV light? Can there be some system put into place to document repeated exposures to UV lamps during the authentication or grading process that would help minimize many of the unneeded and repeated "cooking" under high intensity ultraviolet UV light that our philatelic collections are being subject to.
Of course, as with VISIBLE light, past exposures of our Stamp Art to ultra-violet UV light are "lights" that have passed under the bridge, but with respect to philatelic items of particular aesthetic, history, and value, your responsibility is to minimize their exposure to not only to VISIBLE light, but to all forms of UV light as well.
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