Re: HID Lamp dimming

scott wrote:
I have been approached by a company that markets a dimming system (marketed
as energy reduction system) to install their system on a large exterior
lighting for which I am responsible.

The installation is predominantly 150 Watts and 250 watts HPS shoebox
fittings on a carpark.

There are around 500 luminaires involved in one stage, so the potential to
reduce energy consumption is fairly enticing.

The Australian Standard for carpark lighting allows for a reduction of
illuminance levels after a curfew, so the effect of dimming the lamps will
not cause any graet problems with code compliance.

So far, they have not revealed much in the way of the electrical
characteristics of their system, other than to say that they reduce the
circuit voltage at the distribution board, and retain the existing control
gear and wiring system.

Hi Scott,

Was this an SVC (Sinewave Voltage Conversion) system? These systems
fairly cleanly reduce the output waveform on the dimmer outputs without
using phase chopping (obviously a problem with inductive/capacitive
loads). Generally speaking, they work quite well for a small range
from 100% down to as low as 60% if the system is optimised for their
usage, however, the impact on lamp life is unknown, and I don't know of
any well documented case studies to make up for the lack of science.
SVC dimming may well be the way of the future as the technology costs
come down towards those of phase chopping as it reduces lamp hum,
extends lamp life and manages power factor well. For metal halide?
Not sure yet.

In Australia, you can talk to Dynalite (speak to Laurence Coote) who
have a system I used seven years ago with some success. ETC also do a
system, although I doubt it is optimised for carpark lighting - they're
much more in the entertainment and hotels market.

As the other posters said, demand hard facts - light output effects,
current effects, power factor, lamp life, warranty conditions, shift in
lamp colour, etc.

Also consider the good old "turn half of them off" scenario. Very
effective in my experience. Cuts exactly half of the light output, and
half of the power usage. Alternate which half you turn off night by
night - otherwise half your lamps need replacing twice as often as the
others. Watch your light distribution - you still need to meet code!

All the best with it, and please report back on your conclusions, which
ever way you go.

Thomas Paterson
www.luxpopuli.com

.

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