Short-wave Ultra Violet light is very damaging
to the skin and eyes. Ozone generation is another hazard. This can be produced
by the action of short-wave UV on oxygen in the air.
Lamp operational circuit
Deuterium Lamp
The Deuterium lamp shown on the right operating, emits a
blue-white light. However, these lamps are used to produce Ultra-Violet (UV)
emissions which we can't see. The outer lamp envelope is made form quartz
rather than glass. This is because glass does not transmit short wave UV light.
What makes Deuterium lamps so special, as a UV source, is its continuous
spectrum in the range from 180nm - 300 nm.
Unlike most types of discharge lamp these run on DC and have a pre-heated cathode.
This takes the form of a filament which is initially heated by a low voltage
source. The picture below shows the heater running.
With the heater on, and the lamp voltage applied, the lamp will
not start. A third supply is required to strike the arc and establish
ionisation. The top of the lamp is shown above right with the arc struck. The heater
supply can be reduced or removed at this point as heating is maintained by ion
bombardment, providing the arc current is high enough.
The start or strike voltage is around 400V while the running
voltage is under 100V. The lamp shown here has a designed arc current of
300mA.
A commercial electronic driver for this type of lamp is shown
below on the left. The small block of red LEDs on the top right of the circuit board
indicates the start sequence for the lamp. From right to left LED: 1- Power
available. 2- Lamp supply up. 3- Heater timer 4-Ignition and run-up. 5-Lamp at
full output and heater supply reduced.
Below on the right is the visible spectrum, for this lamp, obtained using a
diffraction grating. This type of lamp is mainly used as a UV source which is
beyond the blue end and invisible to they eye and therefore can't be shown
here.
