From: Dick Stowe (dstowe@FUSIONUV.COM)
Date: Tue, 14 Nov 2001 18:07:05
Ozone is produced when short-wavelength UV (around 180 nm) strikes oxygen molecules in air, creating triatomic oxygen, or ozone. All UV lamps produce a small amount of ozone while operating, but VERY different amounts, depending on the type of lamp and construction.
The reason for the observation that "more ozone is produced when a lamp starts" is the fact that quartz, when cold, will transmit these short wavelengths. During startup, the bulb envelope temperature rises rapidly to its operating temperature (in the range of 850-950 degrees C). At that temperature is has a very low transmission of wavelengths below 200 nm, thereby reducing the ozone generation. Different designs of bulbs and power supplies will have different startup times, from a few seconds for a microwave-powered bulb to a few minutes for some arc lamps.
However, this is not significant, because good light shield design practice is ALWAYS to exhaust the bulb cooling air from the curing chamber, in order to remove heat, volatiles, and any ozone produced. With proper design practice, there are no ozone safety issues.
Ozone should be removed by the exhaust system, so there should not be any odor of ozone in the work space. If there is, the design of the light shielding should be corrected. Ozone generation is only vaguely related to lamp length, and much more a function of lamp type. It is affected by quartz type, fill pressure, additive type, and operating power. Therefore, no generalization of the rate of ozone production will be correct. Most lamp manufacturers will provide data on ozone generation by the type of lamp and operating power.
Finally, there is no economy in running UV lamps when they are not needed. R.W. Stowe