This is the final part in a three-part series discussing setting up a safe work area for your numismatic collection.
Your numismatic work area should include good task lighting. The term “task lighting” refers to lighting designed to supply appropriate illumination to complete a certain task.
A desk lamp is an example of task lighting. The light you choose to examine your collection should suit you and your budget. Lighting can be a very personal choice.
For coins, I prefer an adjustable lamp that allows me to “rake” the light across the surface of the coin. Raking light is very helpful in showing up flaws and condition issues on the surface of the coin.
I personally use an incandescent light source. However, I know that some of my numismatic colleagues swear by fluorescent lights. Low magnification magnifiers with built-in fluorescent lights are readily available and suit many collectors’ needs. Their low cost also makes them attractive.
Light-emitting diodes are a relative newcomer to the lighting industry. The energy efficiency of LEDs has made them quite popular although their relatively high initial cost is an issue with many. Costs have been dropping; LED lighting is worth considering.
The amount of heat (infrared) and ultraviolet radiation given off by a task light should also be considered. Regular readers will remember that light is part of an electromagnetic radiation spectrum that ranges from X-rays at the lower end to radio waves and microwaves at the upper end.
Ultraviolet, visible and infrared are the three components of the spectrum that we need to concern ourselves with. Incandescent lights are quite hot because they are heavily weighted to the IR end of the spectrum.
On the other hand, fluorescent lights are cool to the touch but give off considerable amounts of UV radiation. Incandescent lights emit little UV.
We know that the UV component of the spectrum is highly energetic and damaging to us and many of our collections. It is for this reason that conservators recommend applying UV filters to fluorescent lights. Clearly, there are pros and cons to both lights. LED lights emit very little heat and no UV.
Light and light sources can affect the way that we see color. This could be very important to note collectors.
The lighting industry has developed the Color Rendering Index (CRI), which is applied to fluorescent, metal halide and nonincandescent light sources. CRI is an indication of how a light source renders colors.
The CRI employs a 100-point scale, with natural daylight and incandescent light having a CRI of 100. A CRI of 80 or higher indicates a light source that will give you truer colors. CRI can only be used to compare light sources that have the same color temperature (measured in degrees Kelvin). Lighting experts readily admit that CRI is not perfect and have noted that it is probably not the best system of metrics for LEDs.
As a result, the U.S. National Institute of Standards and Technology has been developing a different system, the Color Quality Scale, which they believe gives a better overall reading of how light sources show true color.
Readers interested in learning more about NIST research should go to www.nist.gov/pml/div685/grp05/vision_color.cfm.
Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.