Stamps Are Art

Protection, Preservation, and Care

What’s a Safe Amount of Light For Your Paper Collectibles? – Part 2

August 12, 2014

In a previous post I introduced you to Blue Wool cards and discussed how you can use them to quantify light exposure without having to invest lots of money in expensive light meters. 

In this post I will show you how you can use Blue Wool cards to protect your paper based collections and collectibles from to being exposed to too much light.  As before, the information in this blog post applies to baseball cards, comics, posters, paper art prints, as well as philatelic stamp art.

As a reminder, Blue Wool cards include rows/stripes of pigmented fabric that are calibrated to indicate cumulative blue wool cardexposure to different amounts of light.  Over time, starting with the top stripe, and working down, each stripe begins to fade based on increasing amounts of light exposure.   An indication that a stripe has begun to fade can be used as an indication of a particular amount of light that the stripe has been exposed to.   In this way, a Blue Wool card placed next to your paper based collectible can be used as an indication of how much light your collectible has been exposed to. This knowledge alone is valuable, but when combined with one other piece of information, Blue Wool cards can be very cheap and powerful tools in the hands of those interested in paper conservation and preservation.   

As I have mentioned, each stripe has particular pigments/dyes that are known to fade in a similar manner to that of known historic items. For example, the 5th stripe from the top is know to mimic the light fastness of of the colors used in many modern 20th century stamps.  Thus, the amount of time it  would take the 5th stripe fade, is the same amount of time it would take for a 20th century stamp to fade when exposed to the same amount of light. The amount of time it takes to cause a stripe to show evidence of fading can be analogized to that of filling of a “light bucket,” with each exposure to light acting to fill the bucket with an added quantity of lux (a measure of the amount of visible light per unit area at the surface of an object where the closer a light source is to an object, the higher the lux will be). 

It is known that the light bucket of the 5th stripe from the top will overflow after about 32 Megalux hours of cumulative VISIBLE light exposure.  Lower intensities of light will of course take longer to fill the light bucket. 

Confused, sets use the chart below to help explain the light bucket concept further. What the chart shows is how much LUX different amounts of typical light emit.

VISIBLE Light Condition
Light at Surface of an Object (Approximate)
Direct Bright Sunlight 100,000 lux
Shade in Direct Bright Sunlight 10000 lux
Direct Bright Sunlight in a room 5000 lux
Halogen Lamp 700 lux
Typical Fluorescent Room/Office Lighting 300-500 lux
Typical 100 watt bulb at a distance of 3 ft 100 lux
Museum Lighting 50 lux for sensitive materials (i.e. stamps)
Wax Candle at 1 ft 10 lux
Full Moon 1 lux

 Effects of Indirect Sunlight

Thus, exposure of the 5th stripe of the Blue Wool cart to the 10,000 lux of indirect full sunlight, 8 hours a day, over 1 year (365 days) would cause the 32 Megalux bucket represented by this stripe to be filled with 10,000-lux x 8 x 365 of lux, or equivalently about 29 Megalux, an amount of illumination that would be just short of causing visible fading of a modern stamp.

Effects of Office or Room Light

The analogy above can be declaration of independenceextended to understand the effects of any lighting condition. Lets consider the cumulative exposures to light that would occur in a typical room/office illuminated by bright fluorescent lamps (500 lux), in which case, with 8 hours of illumination each day for one year, a modern stamp would be exposed to (500 x 8 x 365) or 1.5 Megalux over one year. At this rate, the 30 Megalux bucket of the modern stamp would begin to overflow/fade after about 20 years of cumulative illumination (30 Megalux = 1.5 Megalux x 20 years) under normal office or room light. 

Using a similar calculations, when exposed under 50 lux of illumination (proper museum lighting), even moderately lightfast materials like modern stamps would evidence fading in about 200 years.

If 200 years seems to you to be very far in the future, consider the Declaration of Independence, which is displayed in the National Archives under light conditions that are much less that 50 lux, and but for this low level of light would long ago have faded from existence.

Hopefully you will by now understand how it is that you can use Blue Wool cards to protect your paper based collections and collectibles from to much light exposure.  By placing a Blue Wool card next to your collectible, you can monitor how much light it has been exposed to.  Assuming you know what the light fastedness of your particular treasured item is, you can anticipate whether or not it has reached a point when if will begin fading and protect it, before it does so, by removing it from the light.

BUT, before you quickly conclude that 50 lux, 200 lux, or some other amount of VISIBLE light illumination is an acceptable amount of light you can expose your collections to because the calculations above show that it would take hundreds of years before they would show signs of fading, I advise you to wait for my next post on “What Is a Safe Amount of Light Exposure – Part 3″.   For those of you that can’t wait – the answer is very simple, there is NO safe amount of light exposure for paper based collections.


Will the Superman #1 Comic Book Sell For More than the British Guiana Stamp?
Will the Superman #1 Comic Book Sell For More than the British Guiana Stamp?


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