3.2 Lights: Detail Discussion
Description
This article is from the ReefKeepers FAQ, by several authors (see the Credits section).
3.2 Lights: Detail Discussion
For most aquarium lighting applications, the bottom line is
getting the needed intensity and spectrum of light at the lowest
cost while remaining within aesthetic limits.
A lighting analysis is now presented. Everyone has their own sets
of numbers they would plug in here, for now lets assume the
following for comparison. Many will debate specifics found below.
Feel free to substitute your own numbers, but the methodology is
sound.
Bulb cost and performance:
NO lumens per lamp = 2600 (Phillips F40D daylight, initial)
NO watts per lamp = 40 (ditto)
NO cost per lamp = ~$20 (from memory, DLS actinic day)
VHO lumens per lamp = 5940 (Phillips F48T12/D/VHO daylight, initial
)
VHO watts per lamp = 110 (ditto)
VHO cost per lamp = ~$30 (ditto)
MH lumens per lamp = 36000 (Philips MH400/U, initial)
MH watts per lamp = 400 (ditto)
MH cost per lamp = ~$70 (from memory, Venture 5200K)
operate lamps 12 hours/day
replace lamps once per year
electricity cost = $.09 / KWH (your mileage may vary)
Annual cost per lumen:
cost = ( cost-per-lamp / lumens-per-lamp )
+ ( watts-per-lamp / lumens-per-lamp ) * 12 * 365 * .09 / 1000
NO cost = .0077 + .0061 = .0138 dollars per year per lumen
VHO cost = .0051 + .0073 = .0124 dollars per year per lumen
MH cost = .0019 + .0044 = .0063 dollars per year per lumen
Basically, in fluorescents, the VHO lamps give a higher operating
cost but a lower replacement cost for the same total amount of
light. But it's close, and you should plug in your own numbers to
see what's best for you. If you replace lamps more frequently
then VHO is better, if you pay more for power, NO is better.
There is a greater variety of lamps available for NO than VHO.
OTOH, it seems that NO lamps can be operated at VHO power levels,
with a somewhat shortened lifetime (the higher replacement
frequency is offset by lower lamp cost), so this may not be an
issue.
The initial installation cost (basically the ballast cost) is
higher for VHO, even in terms of per-lumen, but this is a pretty
small part of the total cost of the lighting system over the
years.
NO requires more lamps for a given total light intensity, so you
may not be able to fit enough NO bulbs in your hood if you need a
lot of light.
MH seems to be a winner in both replacement and operating costs,
but there are a couple of caveats. The math ignores the effect of
the ballasts on power consumption, whereas I've measured
fluorescent power consumption as less than the lamp wattage (even
on conventional transformer ballasts) and MH power consumption as
slightly higher than the lamp wattage. The other caveat is just
the EXTREMELY limited choice of spectrums for MH, which is why few
people use MH without any fluorescent.
MH vs fluorescent also gets into the aesthetic and biological
considerations. Water surface ripples causing light ripples in
the aquarium and room are pronounced with MH lighting. Many
people appreciate this effect. Some (e.g. Julian Sprung) feel the
variation in light intensity is actually important for some
photosynthetic organisms.
Many people are under the impression MH runs hot, whereas
fluorescent doesn't. In reality, the efficiencies are similar,
with MH producing slightly LESS heat than the equivalent
fluorescent. The difference is MH dumps all the heat in a small
space so the local temperature rise is greater. But if you want
to try to get rid of the heat it's actually easier to do it if the
heat is concentrated in one spot, since its easier to get rid of a
small amount of very hot air than a very large amount of warm air.
A separate issue, so far only applicable to fluorescent, is the
selection of a conventional ballast vs an electronic one. There is
no doubt the electronic ones are more expensive to purchase, but
the savings in electricity offset the high initial cost in a year
or so. Also, if heat production is an issue, the electronic
ballasts are to be favored. The Icecap VHO electronic ballast is
widely advertised, however its advertised claims are also
frequently questioned. Advance makes a series of NO electronic
ballasts.
There are yet two more issues, for which there are a lot of
questions and too few answers. Specifically, the short term
flicker in light intensity, and radiated electromagnetic fields.
Fluorescent lamps on conventional ballasts flicker at 120 Hz,
which is above the human visual response, so we don't see it
(actually, the flicker is both in intensity and spectrum). But
that doesn't mean other creatures can't see it, or whether they
benefit or are disadvantaged by it. Electronic ballasts cause
flicker at ~30 KHz; it is seriously doubtful that any creature can
detect this, so it would appear constant.
The flicker doesn't have to be visible to have an effect: it
causes any movement to appear strobed, and this may affect the
feeding efficiency of visual hunters.
The fields issue is even more obscure. At least many
cartilaginous fish (sharks, rays, etc) are known to be extremely
sensitive to electric fields, and many crustaceans are sensitive
to magnetic fields (crabs with pieces of magnetite in internal
sensory organs). Fluorescent lamps, with the large area they
cover, tend to radiate (using the term pretty loosely) fairly
strongly, but MH, and the wiring, and the ballasts can radiate
too. It's unknown on how significant this could be in an aquarium
(but its known sharks preferentially attack undersea cables
because of the fields, so there is at least indirect evidence its
an issue worth some thought).
BTW, a grounding device reduces the level of induced voltages in
the tank, but this is achieved at the expense of increased induced
current, so its effect (if any) may depend on the species. Also,
note if you have a titanium coil chiller on the tank, it is probably
already grounded through the chiller, and an additional ground may in
fact increase the electric current. This should not be an issue
with epoxy or ceramic coated chiller coils.
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