Beams of high intensity UV light are useful for curing polymers in certain coatings, such as paints, inks adhesives and the like. Such coatings are often used to treat large surface areas, such as floors and so there is a need to cure coatings on such surface areas with UV light. U.S. Pat. No. 6,761,127 describes apparatus for curing floor coatings using two UV lamps at different wavelengths with energy applied in a linear stripe pattern. This apparatus is said to be limited to no more than 75 watts per inch.
More power density is useful for faster curing. In prior patent application Ser. No. 12/209,080 filed Sep. 11, 2008, G. Wakalopulos described how a known reliable source of UV light at good power is a mercury vapor street light. Typical power is 175 watts per inch available a few minutes after starting. At start-up a small pool of mercury is vaporized and heated. The lamp is a negative resistance device requiring ballast to prevent increasing current from damaging the lamp. The negative resistance is offset by a positive impedance that tends to limit current. As the lamp heats up during operation, internal gas pressure rises and a higher voltage is required to maintain the discharge. The resistive drop across the ballast supplies the required voltage until the required voltage cannot be supplied to maintain the discharge. At that point, the discharge is extinguished, the lamp cools, the gas pressure is reduced and the ballast is again effective once the lamp is started. An auxiliary high voltage electrode is used to restart the arc discharge. Such power in a UV lamp would be desirable for curing floor coatings if heat and electrical stability problems could be solved with appropriate ballast in a convenient radiant energy delivery system adapted for surfaces such as floors. If heat and electrical stability problems are not solved, the lamp fails.