Effects of ultraviolet radiation
Electromagnetic radiation with a wavelength of 10...400nm is called ultraviolet (UV) radiation. Due to practical reasons the UV spectrum is divided into three sub areas:
- UV-A (long wave; Europe: 400nm-315nm)
- UV-B (medium wave; Europe: 315nm-218nm)
- UV-C (short wave; Europe: 280nm-100nm and beyond)
UV-A radiation is also part of sunlight that comes down to earth's surface. It causes different actinic processes, has a noticeable pigment effect, but does practically not cause erythema.
UV-B radiation causes pigment effect and erythema and it forms previtamin D. In most cases this radiation is used for therapeutic purposes.
Short wave (UV-C) radiation has a strong germ-killing effect. It causes erythema and ophthalmitis (pink eye). This radiation can be generated by low-pressure mercury discharge. The nature and the effects of this radiation and the application are versatile.
UV radiation with a wavelength shorter than 200nm is called vacuum UV.
Usually three different kinds of quartz glass or glass are used to manufacture low-pressure lamps:
- non-ozone generating
- ozone generating
- synthetic (strong ozone generating)
The UV transmission of particular quartz glass or glass depends on tube thickness and manufacturer.
Information on different types of low pressure lamps
In general there are four different types of low pressure lamps on the market at present time as summarized in the following table:
(Comparison of different types of low pressure lamps with 15mm tube diameter and 850mm lamp length = dimensions identical to G36T5L)
|low pressure||low pressure |
- HO (high output)
at tube surface
|UV power/lamp length||0.5W/cm||1W/cm||1.5W/cm||1.8W/cm
Pure mercury (Hg) low pressure lamps are more dependant on ambient temperature than amalgam lamps. By adding amalgam the Hg vapor pressure is reduced.
The lamps mentioned above will reach their optimal UV efficiency at the listed tube surface temperatures. The operator has to make sure that this temperature is kept within tight limits. If the lamp is cooled down locally (e.g. by local air beam) mercury may condense and cause early failure.