Fluorescent tubes or lamps are
more efficient and do not produce nearly the amount
of heat standard light bulbs do. To emit light, fluorescent
lamps are filled with a special vapor (usually mercury).
The inside of the lamp is then coated with phosphors.
Turning the lamp on charges the vapor which emits
UV light. The UV light hits the phosphor coating causing
the lamp to produce visible light. Special use and
different types of lamps are made by changing the
coating material. By combining different phosphors
or groups of phosphors lamps can be made that emit
light with certain peaks wavelengths.
Metal Halide lamps are used increasingly
in reef aquariums. They produce a very intense light
and have various color temperatures. Metal halides
work well but have drawbacks. They are less efficient
than fluorescent tubes, get very hot (requiring a
fan to get the heat away from the aquarium and hood),
and are expensive.
General Lighting Guidelines
A commonly asked question is:
how long should the aquarium lights be on each day?
Since most of the inhabitants and plants for aquariums
come from the tropical regions of the world, it is
best to mimic the day-length of this region. Length
of daylight varies little seasonally in tropical areas.
Generally, the light period is 12 hours with an intense
period of 9 to 10 hours. Keeping lights on for over
10 to 12 hours per day is of no practical benefit
and can cause algae blooms. It is best to buy an inexpensive
timer and automate the light system.
Another common question is how
long will the lamps last? Usually lamps should be
changed before they actually stop emitting light.
The reason is that the color spectrum of a lamp changes
as the lamp ages. While the lamp may still light,
it does not emit light of the original wavelength.
A common problem is for the hobbyist to use a lamp
until it no longer radiates light. Lamps should be
changed at least once a year, but preferably every
6 to 8 months. If, for seemingly no reason, your aquarium
starts to grow algae, think about when was your last
lamp change? If it was over 6 to 8 months, consider
that the lamp's spectrum may have shifted and the
lamp needs changing.
The deeper an aquarium or the
more particulate material in the water, the more light
that is absorbed and/or scattered, so less reaches
the gravel or tank bottom. This is an especially important
consideration in plant and reef tanks. Consider adding
an extra lamp for each 15" of tank height over
Lights for different tanks set-ups
Fish-only tanks can have a very
simple light system. The purpose is to show off the
fish and tank setup. The final decision depends upon
the individual taste of the hobbyist. For 20 gallon
tanks and under, one fluorescent lamp is adequate.
From 30 to 55 gallons, two lamps, minimum, should
be used. Add an additional lamp for each 20-25 gallons
of water capacity. A lamp with a 5,000 ¡K to
6,000 ¡K color temperature is recommended, but
many hobbyists prefer lamps which emit more red color
as they can show the fish colors better. This is fine,
but these types of lamps will not promote the growth
Plant tanks require the correct
lighting to be successful. The number one reason for
lack of success in growing plants in an aquarium has
to be the use of the wrong lamp. Plants have two types
of chlorophyll, a and b. Chlorophyll a absorbs light
at 405 and 640 nm. Chlorophyll b has a peak absorption
at 440 and 620 nm. Plant lamps are designed to emit
light at the red wavelengths to duplicate the job
of the sun. But too much red color can cause aquatic
plants to grow tall and thin. For best results, use
a daylight (5,000 ¡K) lamp such as an Aquasun,
Ultralume 50 or Chroma 50 in combination with an actinic
white or actinic day lamp. The actinic day or white
lamp is a mixture of 50% actinic (blue light) and
50% daylight. In large or deep aquaria consider using
HO or VHO lamps.
To have a successful reef aquarium,
adequate light is absolutely required. Reef tanks
contain soft and hard corals which harbor zooxanthellae.
The zooxanthellae (symbiotic algae) must thrive in
order for the coral to live. To do this they need
the correct amount of light (intensity) at the right
wavelength (peak absorption). Actinic lights provide
a concentrated light wavelength that promotes photosynthesis.
If only actinic lamps are used, however, the water
color in the tank will be very blue which is not visually
appealing and the light is not intensive enough for
the other processes of the aquarium inhabitants. Therefore
a reef tank should have a combination of one actinic
lamp and one or two daylight lamps for each 30 gallons
of water. The daylight lamp can be either a metal
halide bulb or daylight fluorescent lamp (preferably
HO or VHO). The color temperature of the bulb or lamp
should be 5,000 to 6,000 ¡K.
The other popular type of reef
system is to combine metal halide lamps with the fluorescent
lamps discussed above. Figure on one metal halide
per 25 gallons of water for a really successful reef
Generally, not much attention
is paid to the lights for a freshwater fish-only aquarium.
It seems only a little attention is paid to the lights
for tanks where the goal is to grow plants. If you
have algae problems, or plants that won't grow, or
corals and anemones which waste away after 3 or 4
months, suspect improper lighting as the cause. Discuss
the specifics of your tank (size, shape, total gallons,
etc.) with your favorite store clerk. Listen carefully
to the suggestions he/she makes, do they make sense?
The right light can mean the difference between success
and failure of your aquarium. □
© 1998 Dr. Timothy A. Hovanec