Metal Halide efficiency/rated lifeD
Recently I followed up on a posting by Stephen Parry and ordered
a copy of "The Metal Halide Source Book - Catalog and Technical
Guide" from Venture Lighting International. It does contain a
wealth of information.
This guide mentions that although Universal lamps (the ones with
the /U designation such as the Coralife 5500K) can be burned in
any position, they sacrifice life expectancy by 25% and lumen
output by 25% when burned in the horizontal position as opposed
to the vertical, base up position. This may be of interest to
people who must decide between the shoe box type hood and the
hanging spotlights. The former holds the bulb horizontal to the
water surface. the latter has it perpendicular. There is also a
much greater chance of violent failure of the bulb in the horizontal
position. Maybe some of us are not getting the output and longevity
we deserve from metal halide.
Also referred to was the ubiquitous colour shift that occurs with
time in all metal halide lamps. This is 200K to 300K by the end of
their economic life and up to an additional 600K near the end of
their rated life. Each bulb type shifts uniquely, although the
authors do not elaborate.
For the MH175/U/5K (5200K) average life was 7500 hours, which means
that the economic (useful) life is 4500 hours (60% of 7500). CRI
is 75. The initial lumens/watt (measured after 100 hours) is 68,
and the mean lumen output is 9000. A year and a quarter at 51
lumens/watt. In the horizontal position, a year at 43 lumens/watt.
The 250 watt and especially the 400 watt bulbs were more efficient.
I ordered a 4300K MH bulb from TFP. How have people found it for
planted tanks compared to the Coralife 5500K?
Some horizontal high output metal halides have mean outputs of
80. These require a special socket. There are also regulated lag
ballasts that deliver 90 plus lumens/watt from those bulbs designed
to run on them. In addition there are vertically oriented lamps
that operate on the regular CWA ballasts that get as much as 90
lumens mean output. All of the above are 4000K lamps and have much
higher life expectancies. My question is, How the hell do Coralife
and other purveyors of expensive lighting "solutions" get away with
selling such inefficient short-lived lamps? The answer is that it's
cheap and easy to offer one type of bulb (universal), not two, and
no one complains. I guess if someone can afford to spend $800 on a
hood, Hamilton or Coralife figure an extra hundred or two per year
won't mean much to them.
The premise upon which the above rant is based is that the Coralife
5500K lamps are made by Venture and/or the same general principles
of bulb construction and output as described in "The Metal Halide
Source Book" apply.