Information

Technical information on reducing the wattage of high intensity discharge lamps, Feb.2009 Page 5 of 5
3. Recommendations for reducing the wattage of High Intensity
Discharge lamps
High pressure mercury lamps
These lamps can be dimmed to 50 % of the rated
wattage, whereby they must start up with 100 %
wattage. Dimming is possible by voltage reduction,
phase control and amplitude modulation.
High pressure sodium lamps
All VIALOX
®
NAV
®
lamps can be operated at 50%
of their rated wattage without negative impact on
lifetime through
 step switching by changing to inductive control
gear with the next lower rating
 step switching with additional inductance,
whereby in both cases electronic power switches
have to be used.
The lamps must be started at rated wattage and
must operate at rated wattage for about 10
minutes before reducing lamp power.
Lamp power must not be reduced by lowering the
mains voltage or leading edge phase control.
OSRAM recommends for dimming the electronic
control gear POWERTRONIC
®
PTo.
Metal halide lamps
POWERSTAR
®
HCI
®
(cylindrical arc tube) and
POWERSTAR
®
HQI
®
Reduced wattage operation of POWERSTAR
®
HCI
®
(cylindrical arc tube) and HQI
®
lamps is not
permitted as this could result in considerable
deviations in color, poorer maintenance and
reduced lamp lives.
POWERBALL
®
HCI
®
Basically it is possible to dim POWERBALL
®
HCI
®
.
While the higher thermal load capacity of the
round ceramic permits better dimming behavior in
luminous efficacy and color rendering compared
to metal halide lamps with quartz arc tube or with
the normal cylindrical ceramic, dimming still
causes a shift in color coordinates. Dimmed lamps
show in general a somewhat stronger drop in light
output and a wider color spread through-out the
life of the lamp.
OSRAM therefore recommends not to reduce
power with currently available lamps on conven-
tional control gear, as dimming here changes the
properties of POWERBALL
®
HCI
®
.
If the lamp is still to be dimmed, it is recom-
mended that only adjustable electronic ballasts
with square wave operation are used for this
purpose. The wattage can be reduced by at most
by 50% of the rated lamp wattage.
In any case, the lamp must be run with 100 %
wattage for at least 15 minutes after switching on,
so that the lamp lights up correctly.
Generally we accept no warranty for dimmed
POWERBALL
®
HCI
®
. Only when POWERBALL
®
HCI
®
are dimmed on POWERTRONIC
®
PTo we
accept a warranty regarding lifetime of the
lamps.
Operation of POWERBALL
®
HCI
®
on
POWERTRONIC
®
PTo:
The combination of POWERBALL
®
HCI
®
lamps
and POWERTRONIC
®
PTo allows an energy
saving operation, where optimal color representa-
tion is not of importance - like in outdoor lighting.
The PTo with square wave operation and opti-
mized ignition operates the POWERBALL
®
HCI
®
lamps in the best possible way down to 60 % of
the rated lamp wattage. There will be no signifi-
cant negative effects when dimming.
Operation between 85% and 60 % of the rated
lamp wattage has also no negative influence on
failure rate. Lamp color, however, tends to shift
then slightly to greenish and the colors between
the lamps can differ (color spread).
Luminous flux decreases a little more over lifetime
than with 100 % operation at the PTo. This effect
can be reduced by mixed operation between
reduced power and 100 % of the rated lamp
wattage.