There are three main types of aquatic plants: terrestrial plants that grow out of water, submerged plants that grow completely underwater, and emergent plants that grow above the water but need their roots submerged. Plants need three essential components to survive: light, a source of carbon like carbon dioxide, and nutrients. When choosing lighting for an aquarium, factors like photosynthetically active radiation, color rendering index, and color temperature should be considered to best mimic the sun's natural light output for plant growth.

2. There are several different types of plants available. Some with which we are
most familiar grow wholly out of the water (terrestrial) while others prefer to be
completely submerged beneath the water (submersed), while still others will
grow and flower above the surface of the water, yet their root systems are at
great risk of drying out if planted above the water line. These plants are
generally referred to as emersed plants.

3. Plants need 3 essential components
for survival. The obvious first one is light.
Light comes from different sources,
with the sun being by far the most
powerful and of course the light by
which all plants have evolved and
adapted to suit.
The second thing plants need is a
source of carbon. This is generally
obtained from Carbon Dioxide (CO2)
Finally plants need a source of
nutrients. Elements such as nitrogen,
phosphorous, and potassium are
crucial as well as a wide range of
other ‘trace’ elements.

4. Did you know? The sun’s
output is approximately 527
watts of infra-red, 445 watts of
visible light and about 32 watts
of U.V. light at it’s peak… for
every square metre of ground
on earth!
 There are many factors to consider when lighting your
planted aquarium. Light is not all created equally. For
our aquatic plant needs, let’s discuss some of the
basic requirements for tank lighting and good
underwater plant growth. Our aim is to reproduce
the sun’s natural light output as faithfully as possible.

5.  What in the world are we talking about? And what the hell do
all those letters mean? And why are you talking about
temperature. The only light I know of are light bulbs and the
sun and they are only one temperature – HOT!
P.A.R. – Photosynthetically Active Radiation is a measure of the spectral
range of the sun’s radiation which is able to be utilized by plants. Any
photons of light outside this range will not trigger photosynthesis within the
plant due to incorrect wavelengths.
C.R.I. – Colour Rendering Index is the light sources ability to faithfully
reproduce colours within the correct spectrums for optimum plant growth
and function. Plants use predominantly red and blue light for
photosynthesis.
Colour Temperature is usually measured in Kelvin and will appear on
most light packaging that you buy for your aquarium. For all intents and
purposes it is worth noting that the higher the colour temperature
(Kelvin), the more blue the light will appear to the human eye and the
lower the temperature, the more red it will appear (useful for making
red plants SHINE!)

6.  It can be a daunting thing to walk into your local fish
shop and stare at the rack filled with umpteen
different tubes in various sizes, shapes and colours.
Take note of the size and type of tube that your light
fitting will take before shopping. The most commonly
available lights available in the industry today are:-
Fluorescent
Compact Fluorescent
High output and Very high output
Metal Halide
LED

7.  For most people growing a few plants is enough. In
freshwater aquariums most local fish stores will carry a
range of fluorescent tubes known as grow tubes. On the
side of the box the tube comes in there is often a few key
bits of information. As discussed earlier there will probably
be a Kelvin rating which will dictate how blue/red your light
appears.
There will also sometimes be a CRI index graph that will show
you specifically where that particular light ‘spikes’ in the
colour spectrum. Ideally you should be looking for spikes in
the blue and red part of the spectrum to cover all your plants
requirements.
Finally, ensure that your light is the correct length and
wattage for the unit you intend on installing it in. As a very
basic measurement, the total amount of light your tank will
need can be considered using this equation. 1W of
aquarium light for every 4 litres will be sufficient for most low
tech plant setups.