The goal of this tutorial is to clarify issues that are relevant to a

Understanding the difference between UVB and UVA radiation
UV specification background information for Museums
What is being done particularly for Museums?

Understanding the difference between UVB and UVA radiation

It is well known that light has a Wave-Particle Duality. That is, light exhibits both particle and wave properties at the same time. In 1923, Compton verified that a photon hitting an electron is like a billiard ball collision. There is a momentum transfer from the photon to the electron which manifests itself as a wavelength shift. Compton used X-ray photons of known wavelength and found that the scattered photons had longer wavelengths. The shift to a longer wavelength provided proof that the initial momentum of the photon was partially transferred to the electron.

In 1905 Einstein proposed that light consists of "light quanta" that have energy E=hc/x where h is Planck's constant (4.14x10^-15 ev*sec) , c is the speed of light (3.0X10^8m/sec), and x is wavelength. Using Einstein's equation: 300nm radiation contains 4.14 ev (electron volts) per photon where as 380nm contains 3.27 ev/photon.

Let us use Compton's billiard ball and perhaps a soft ball of the same size and shape to illustrate an important point. If a window can generally withstand a force of 30 pounds per square inch (psi) and a billiard ball can generate up to 35 psi as opposed to a soft ball which can only generate a maximum of 29.0 psi, it doesn't take an Einstein to realize that while a singe billiard ball will break the window, it may take hundreds of tries with a softball before finding the weak spot in the window. Likewise with UVA (soft ball) radiation, you can expose certain materials to it with little or no damage ever occurring. In addition,according to the Lighting Handbook Reference and Application , Copyright1993, "It has been found that ultraviolet energy of wavelengths shorter than 300nm (UVB) may cause rapid fading and other forms of product deterioration in some cases."

UVB is not only more harmful to materials but also is potentially more harmful to the human eye. A condition known as Photokeratitis is a painful inflammation of the outermost layer of the cornea. The action spectrum (highest absorption) peaks at 270-280 nm, falling off to negligible values at 320 nm. In addition, recent studies have also shown "statistical significance" in the relationship between cortical lens opacities (cataracts) and lifelong UVB exposure.

UVB radiation ("B" for "Bad") is clearly the most harmful radiation both to man and materials. Fortunately, SoLux, has the least amount of UVB radiation of any light source on the market, 2.4 Microwatts/Lumen.

UV specification background information for Museums

The 75 microwatt per lumen standard was derived from the work of G. Thompson, The Museum Environment (London: Butterworths, 1986). The 75 microwatt per lumen standard is based on the output from a standard incandescent lamp. Subsequent work, by D.R. Saunders, UV filters for Museum Light Sources (National Gallery Technical Bulletin) suggests total levels of 10 microwatts per lumen. In a recent article by Kevan R. Shaw, Lighting Dimensions (September 1996), Mr. Shaw states what he believes should be the considered for Lux and UV limits. "Max level sensitive (materials) Lux 100, microwatt per lumen 10, Max level normal Lux 200, microwatt per lumen 40."

Since the above values are simply guidelines and not standards, many museums to be on the safe side with their priceless artifacts do not discriminate between UVA and UVB radiation they simply want zero UV. New 3500K and 4100K SoLux lamps have been designed with the museum market in mind with the lowest possible UVB and UVA output.

Learn more about choosing the proper daylight color temperature for museum lighting by reading Daylight: Is it in the eye of the beholder?

The new SoLux daylight color temperatures (3500K and 4100K) have been available
for over two years now and have quickly become the most specified light sources
in the museum world.

Author: Kevin P. McGuire

## SoLux Applications

Solux is used in numerous applications all over the world. Here are just a few:

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