The following unedited text was originally written for inclusion in
         the May/June 1990 issue of Aquarium Fish Magazine. It is presented
         here by the kind permission of the editor, Edward Bauman. This
         article may not be reprinted in any form without the express
         permision of AFM and the author.


Reef Aquarium Lighting for Healthy Invertebrates
by J. Charles Delbeek B.Sc., B.Ed., M.Sc.

This is probably the one topic about which the most arguments exist;
which type of lighting is best to use for reef tanks? I imagine you
think that I'm going to tell you which is the best right? Nope ...
wrong! There is no "best" type of lighting simply because all corals,
unlike man, were not created equal. The problem lies in the fact that
there is a great deal of variability within one species of coral.
Both coral shape and colour can vary drastically depending on what
depth they live at or under what light conditions (i.e. shade vs.
light) they develop under. This results in two specimens that may
look completely different and subsequently, have different lighting
requirements, yet belong to the same species. It is this fact that
has made coral taxonomy historically difficult and has posed numerous
problems for aquarists.

The choice of lighting to use contains numerous variables that must
be taken into consideration. The first of these is the type of
invertebrates you wish to keep. If you would like to keep
invertebrates that rely on their symbiotic algae (zooxanthellae) for
their nutrition, then light intensity and spectrum are important. If,
on the other hand, you want to keep invertebrates that lack
zooxanthellae such as Dendronephthya spp. soft corals, Orange Sun
Coral, Tubastrea aurea or certain gorgonians, the lighting is less
critical. Another variable is the natural habitat that the coral was
collected from. Deeper water corals (>30 ft.) do not require the
intensity of light that shallow water forms require and do not need a
complete spectrum of light to do well. Shallow water (<15 ft.) forms
require greater intensity and a wider spectrum of light than other
forms. The greatest decrease occurs in the red end of the spectrum
within the first 10 m (30 ft) with maximum transmission occurring at
a wavelength of 480 nm (blue light). Intensity drops off dramatically
with depth too (see Moe, 1989). I believe that it is these facts
which have sparked the intensity vs. spectrum debate amongst
hobbyists. Hobbyists don't seem to take this into consideration when
purchasing and placing new corals in aquariums. They may put newly
acquired pieces directly under their metal halides and watch them
open up wide for a time then slowly wither away. Transplant studies
have shown that corals taken from deep water and placed in shallow
water die-off rather quickly while those moved to deeper water from
shallow water, grow more slowly and change form (Dustan, 1982). We
will go into why this occurs in a moment.

Lets first take a look at the two main forms of lighting available:
metal halide (HQI) and fluorescent. Before I begin I would like it
made clear that I am not endorsing one form of lighting over another.
I will simply supply you with the information that I have obtained
from various sources and my own experience. Take this information,
read whatever else you can get your hands on and then make your own
decisions. Forms of lighting that are definitely not recommended for
reef tanks are mercury vapour and sodium vapour lights as well as HQL
and HQI-NDL lighting which have colour temperatures (4300K) and
spectrums that are unsuitable.

Metal halide lights have been blamed for many things, much of which I
think can be traced to four factors: improper bulb choice and
placement, inadequate shielding and poor specimen placement. The
choice of bulb is important because many of the HQI lights sold early
on had colour temperatures of 5000 K or less which lacked sufficient
blue and had too much yellow and/or red. The spectrum of these bulbs
was not really suitable for reef aquariums but were often recommended
by those who considered intensity to be more important than spectrum.
Other bulbs (i.e. Energy Savers 5500 K and Osram D 5200 K which are
used in some Dupla fixtures) have higher temperatures (>5200 K) and
provide more blue. Although some (Thiel, 1988) maintain that HQI
lamps alone give enough blue I don't feel this is true; even better
success can be achieved by using a pair of HO or VHO actinic bulbs in
conjunction with the HQI. It has been shown that blue and white light
promote greater skeletal growth in hard corals, and their isolated
zooxanthellae, than green or red light (Kinzie et al., 1984).
Therefore, additional blue light will only have beneficial results
and should be favoured over the addition of higher intensity lights
that have more red or green light.

Wattage is important too. Obviously one must take into consideration
the type of invertebrates one wishes to keep, at what depth they
normally occur and the size of the tank before selecting the wattage
of bulb to acquire. Another factor might be the degree of heating
that the light will cause in the tank; metal halide lights should be
at least one foot above the water surface to prevent overheating of
the water. Some European aquarists recommend that one 250 W HQI lamp,
at a height of 35 in. (90 cm) above the bottom of the tank, is
sufficient for a tank length of 35 in (130cm) (D. Stüber, personal
communication). I can't help but think that many recommendations on
the amount of light required have focused on studies of light
intensities found at a depth of a few metres (see Sprung 1988). What
has failed to be taken into consideration are the following facts.
First of all not all our aquarium specimens come from such shallow
areas and have no need of such high intensities. Secondly, even in
these shallows, the light intensity is far from constant. Light
intensity gradually increases over the day, peaking between 1100 and
1400 hours, after which it gradually decreases again. Therefore, high
intensity light is only present for a few hours per day. Thirdly, the
affects of clouds and weather greatly reduce the amount of light that
eventually reaches the water surface, therefore the number of hours
and days when the reef actually receives the maximum amount of light
available is actually quite small. Wilkens and Birkholz (1986)
recorded the lux readings at a depth of 1 m on a reef in Indonesia.
They found that values ranged from a low of 2 800 lux in the morning
to 14 000 lux by 1100 hrs. and fluctuated after that point, due to
intermittent sun and cloud, between values of 17 000 and 22 000 lux,
with peaks of 26 000 lux from noon till 1400 hrs., falling quickly
again in the late afternoon to values between 9 000 and 7 200 lux.
These values would be strongly attenuated with depth and suspended
particles in the water caused by the turbulence from waves and tides,
such that intensities will drop off drastically within the first 5 to
10 metres (see Dustan, 1982). In the relatively particulate free, low
dissolved organic carbon content water that exists in properly cared
for aquariums, the amount of light fall-off may be negligible.
However, measurements by Thiel (1989) and Burleson (personal
communication) have shown that a significant drop-off in intensity
actually does exist, even in relatively shallow aquariums. This must
be taken into consideration when deciding upon the size of bulb to
obtain and the overall design concept of the aquarium (i.e. types of
organisms and their placement). Finally, the greatest variety of
coral growth occurs at depths bewteen 30 and 40 ft. (10-15 metres)
where light intensities are much lower than 20 000 lux (see Dustan,
1982).

As has been reported elsewhere, HQI lighting produces ultraviolet
(U.V.) light which can be harmful to those corals that lack
appropriate U.V. shielding pigments (Mohan, 1990). This can be due to
the fact that they were collected from deeper water or that they have
lost these pigments during shipment/captivity. Add to this the fact
that many fixtures were sold with inadequate U.V. shielding and you
can see how reports of HQI lamps burning corals could come about.
Another interesting possibility is the infrared range. Do HQI lights
put out large amounts of I.R. and could this possibly damage coral
too? This is currently being studied by some hobbyists (J. Sprung,
personal communication). HQI lamps that are not encased by glass
(e.g. Osram HQI lights) must be used in fixtures with U.V. shielding
while bulbs already encased in U.V. absorbing material (e.g. Energy
Savers) should still have some sort of shielding to protect them from
water splashes. Do not be concerned if small amounts of U.V. are
still transmitted, since the majority of zooxanthellae containing
invertebrates require this U.V. to maintain their U.V. blocking
pigments and fluorescent colours.

Coral placement in the tank is another important factor. When putting
new specimens into a tank they should NOT be placed directly under
the HQI light! Many a well-intentioned aquarist has reasoned that
they are rejuvenating their corals after a period of "mistreatment"
in a dealer's tanks. This is similar to running out on the first
sunny day in the spring and lying in the sun for 8 hours hoping to
make up for lost light and vitamin D synthesis deficiency acquired
during the winter. You quickly damage your skin because it has not
had a chance to build up the necessary pigments to protect itself.
The same can occur with corals. The chloroplasts in the zooxanthellae
of corals behave in a similar manner to those found in plants. When
faced with lower light levels they produce more chlorophyll and when
faced with too much light they will reduce the level of chlorophyll.
Plants growing under the canopy of a forest have broader, darker
green leaves than the same species of plant growing in the full
sunshine. Corals are no different. If exposed to lower light levels
they become darker brown in colour and their growth form becomes more
elongated and tabular in an attempt to increase their surface area.
Those corals from shallow water tend to be lighter brown in colour
and most have U.V. absorbing pigments that can, in some cases, give
them beautiful fluorescent blues and greens (Mohan, 1990). By placing
corals that have become low-light adapted or light starved for a
period of time, in a brightly lit tank you run the real risk of
light-shock which may damage the coral beyond its capacity to repair
itself.

Another potential problem could be oxygen poisoning. When deeper
water corals are placed under brighter light, their zooxanthellae
produce greater amounts of oxygen. Under these high concentrations
oxygen can easily poison both corals and anemones (Dykens and Shick,
1984; Wilkens and Birkholz, 1986). The response is often for the
coral to quickly expel their zooxanthellae (Wilkens and Birkholz,
1986). Shallow water anemones cope through various mechanisms
including the use of enzymes to break down oxygen, withdrawing their
tentacles, covering their body column with gravel to protect it from
the sun and to seasonally vary the amount and ratio of chlorophyll in
their zooxanthellae to correspond with seasonal changes in light
intensity (Dykens and Shick, 1984). Similar behaviour may exist in
corals.

When placing newly acquired corals into a HQI lit tank, they should
be put in the lower regions away from direct light. Gradually, over a
period of a few weeks, they can be moved closer to the light.
Falkowski and Dubinsky (1981) found that the Red Sea coral,
Stylophora pistillata, required 4 weeks to adapt from shade to
light conditions when transplanted. Most Leather corals
(Sarcophyton and Lobophyton) and other soft corals such as
Sinularia sp. can withstand direct HQI light since they contain
high levels of U.V. absorbing pigments and come from shallower water
(Wilkens, 1987). Most hard corals offered for sale in North America,
however, come from deeper water, from shaded areas or from turbid
shallow waters (e.g. Catalaphyllia [Elegans Coral], Euphyllia
[Hammer Corals]) and should be gradually acclimated to HQI lights.
Shallow water, reef building species such as Acropora spp. require
higher light levels and can do very well under the right conditions.
However, Dustan (1982) found that specimens of the hard coral
Monastrea annularis, that were transplanted from 30 m to 15 m,
exhibited greatly reduced growth rates, algal bleaching and suffered
high mortality over a 2 year period. Dustan (1982) concluded that
there may be ecotypes of zooxanthellae such that those adapted to
high light intensities function poorly in deeper habitats, while deep
algae ecotypes are damaged by the higher light intensities of shallow
water. If this is correct, then certain hard corals that are
collected in shaded or deeper waters, may never be able to adjust to
the increased light intensities of HQI lit aquariums. This may
account for the reports of poor coral behaviour under intense
lighting. Another problem has to do with duration. When putting HQI
lights onto an existing aquarium for the first time, the lights
should only be on for a few hours a day. This time period can
gradually be increased as the animals adapt to the higher light
levels. If you use more than one HQI light they should come on in
stages with all the lights being on for only 2-4 hours and then
sequentially turned off over a period of a few hours. This can
gradually be increased to a maximum of 5-8 hours per day. These
recommendations apply to other high intensity lights such as VHO
fluorescent lamps.

One thing that I would like to explore is whether the increased light
levels of HQI light increases calcification rates. There are numerous
studies that have demonstrated that calcification rates in hard
corals are dependent on light energy and that light-enhanced
calcification appears to be essential to the construction and
maintenance of coral reefs (Dustan, 1982). It is entirely possible
that, under intense HQI or VHO lighting, the corals may remove
calcium from the water at such a rate that they quickly deplete the
level of calcium ions and begin to suffer. This may be why HQI
lighting, used in conjunction with the regular addition of calcium
hydroxide and strontium chloride (an essential element in the
calcification process) solutions, has resulted in greater success in
keeping hard corals in Europe. The lack of such additions, combined
with the other factors described above, may explain the apparent
inconsistent success of HQI lighting in maintaining hard corals in
North America.

Fluorescent lights are quite handy to use since they are easily
installed and maintained by the average hobbyist, and they are less
expensive. There are so many different types of bulbs available that
a hobbyist, who takes the time to do the research, can easily develop
a combination that will duplicate the exact spectrum they want. The
intensity of some fluorescent combinations can even match those of
most HQI sources, especially when used in conjunction with properly
designed fluorescent lighting reflectors. This invariably means using
high output (HO) or very high output (VHO) lamps since using the
regular output bulbs would require so many bulbs that you couldn't
fit them all above a tank. When using HO and VHO bulbs you must be
aware that some of these can also produce potentially harmful U.V.
and should be shielded appropriately. One of the problems with
fluorescent light sources is that both their intensity and spectrum
change with age. This is especially true of HO and VHO fluorescents.
The decrease in intensity could cause reduced growth rates of both
corals and algae, while the spectrum usually shifts towards the red
end which can lead to breakouts of undesirable algae. These bulbs
should be replaced at least once every six months, even more
frequently if reef-building hard corals are kept. The accepted
recommendation for fluorescent lights has been to use a combination
of Daylight and Actinic type bulbs, primarily to ensure a spectrum
heavy in the end blue and low in the red (Burleson, 1987). However,
there are now a number of fluorescent lights that make various claims
about the suitability of their spectrums for reef aquariums. One
must, of course, use one's own judgment and rely more on facts than
advertising copy. Try to obtain spectral output charts for the bulbs
you are interested in as well as information on their colour
temperature and colour rendition. Look for bulbs with high Kelvin
ratings (>6000 K), good colour rendition index (CRI) and an efficient
lumen to watt ratio. Moe (1989) gives a complete listing of the more
common fluorescent lamps, including the above information. Pay
special attention to the amount of U.V. radiation produced and take
necessary precautions. One may have to by-pass the distributor and go
directly to the manufacturer to get the information. If no one will
supply you with the information you need, then look for other bulbs.

In summary, I have seen many beautiful tanks lit by both types of
lighting; HQI and fluorescent. I do not agree with those who say
success with hard corals cannot be attained with HQI lighting for I
have seen otherwise! HQI lighting gives excellent results with both
soft and hard corals WHEN USED PROPERLY. I have seen aquariums that
have beautiful, vibrant hard coral growths under HQI lighting and
under a combination of HQI and intensely blue bulbs such as the
Philips Actinic 03 bulb. Leather corals can grow to fantastic sizes
with HQI lights and with HO and VHO fluorescents. The key seems to be
a proper combination of intensity and spectrum. Providing intensity
for simply intensity's sake is counter-productive if the proper
spectrum is not provided also. When the proper spectrum is provided
most organisms do quite well but if the intensity of that spectrum is
increased then their growth rate increases substantially.
Fluorescents are cheaper but their frequent replacement time may make
them more expensive in the long run than HQI which should be replaced
once/3 years although some German hobbyists replace them at the rate
of once every 6 months. If you look at a new metal halide bulb and
one a year old bulb, you can readily see the difference in intensity
after only one year. Therefore, replacing them at least once a year
for soft corals and once every 6 months for hard corals may not be a
bad idea. A word of advice about replacing high intensity bulbs. Make
sure your fixture can be raised. When putting in new bulbs you will
be increasing the intensity of the light and the corals may react
negatively. By raising the bulbs you decrease the intensity and give
the corals a chance to re-adapt. Over a period of a few weeks you can
slowly lower them again. As an alternative, Wilkens and Birkholz
(1986) recommend that HQI lights be shielded with white translucent
plastic to reduce their intensity when introducing new animals or
replacing new bulbs, until the animals have a chance to readjust.

When the proper lighting is obtained you will find that your aquarium
and its inhabitants will look more vibrant and alive. However, this
can quickly change if appropriate water quality and nutritive
conditions are not maintained by the aquarist. This is a serious
hobby and if you are not prepared to devote the time and energy
necessary to maintain these systems then stay away from them.
Advertising copy that claimed that these systems were maintenance
free were highly misleading, however, once your system is running
properly it takes only weekly or monthly chores to keep it
functioning that way. The key lies in observation. Watch your tank
closely every day and look for the slightest changes. It may be
nothing or it may be the start of something bigger. Better to
identify it early so that you have more time to correct it before the
problem gets out of hand.

References
Burleson, J. 1987. Miniature reef aquarium
lighting. Seascope 4 Fall:1-2.

Dustan, P. 1982. Depth-dependent photoadaptation
by zooxanthellae of the Reef Coral Monastrea
annularis. Marine Biology 68:253-264.

Falkowski, P.G. and Z. Dubinsky 1981. Light-shade
adaptation of Stylophora pistillata, a
hermatypic coral from the Gulf of Eilat. Nature
289:172-174.

Kinzie, R.A., P.L. Jokiel and R. York 1984.
Effects of altered spectral composition on coral
zooxanthellae associations and on zooxanthellae
in vitro. Marine Biology 78:239-248.

Moe, M.A. 1989. The Marine Aquarium Reference:
Systems and Invertebrates. Green Turtle
Publications, Plantation, FL.

Mohan, P.J. 1990. Ultraviolet light in the marine
reef aquarium. FAMA 13(1):4-6,156-160.

Sprung, J. 1988. Captive Reefs. Tropical Fish
Hobbyist, October 1988:72-84.

Thiel, A. 1988. The Marine fish and Invert
Aquarium. Aardvark Press, Bridgeport, CN.

Wilkens, P. 1987. Niedere Tiere: Steinkorallen,
Scheiben- und Krustenanemonen. Engelbert Pfriem
Verlag, Wuppertal.

Wilkens, P. and Birkholz, J. 1986. Niedere Tiere:
Rohren-, Leder-, und Hornkorallen. Engelbert
Pfriem Verlag, Wuppertal.