**Lighting Section: The Primary Condition for Aquatic Plant Cultivation**

Lighting is the primary condition for the growth of aquatic plants. Without photosynthesis, it is absolutely impossible to cultivate aquatic plants.

**Photosynthesis in Aquatic Plants:**

Aquatic plants absorb light energy and use carbon dioxide and water as raw materials to synthesize sugars. The light source is the medium that initiates photosynthesis, while carbon dioxide and water are the ultimate participants in the process.

**Lighting Duration:** 

The optimal lighting duration is 8-10 hours per 24-hour cycle. Too short a duration affects growth, and too long can also reduce the efficiency of photosynthesis. The reason is that prolonged photosynthesis accumulates excess sugars that cannot be consumed in time by respiration, leading to an overabundance of sugars within the plants, which affects the photosynthetic reaction. Lighting duration should also be relatively fixed. It is best to install a power timer (also known as a time-controlled switch) to automatically control the lighting without worrying about turning the lights on and off daily.

**Light Intensity:**

The higher the luminous efficiency of the lighting fixture, the more light it produces per unit of power, which we refer to as greater light intensity. For example, a 40W fluorescent tube has a higher light intensity than a 30W one.

**Light Quality:** 

The visible light in the solar spectrum is a composite light composed of seven monochromatic lights: red, orange, yellow, green, blue, indigo, and violet. Artificial lighting produces composite light of varying qualities due to the different intensities of the monochromatic lights that make it up, which is known as light quality. For aquatic plants, simply put, red and blue lights are most suitable for photosynthesis.

**Color Temperature and Color Rendering:**

Color temperature and color rendering are only related to the visual perception of lighting effects and have nothing to do with photosynthesis; they are merely needed for landscape lighting. The higher the color temperature, the brighter the light color. Lights with higher color temperatures generally have higher green light intensity, which may be detrimental to aquatic plants during their cultivation. Color rendering refers to the degree to which artificial lighting reflects the visual color of an object close to its actual color, with 100 being the highest, i.e., 100% reflection of the object's actual color. Achieving 100% color rendering with artificial lighting is actually unrealistic. Therefore, it is sufficient to equip one effect light in a set of aquarium lights, and it is not advisable to have too many. Lights with a color temperature below 3000K appear yellow and warm; those around 5000K appear blue and have a cool feeling. Plant lights generally have a color temperature of around 1000K.

**Types of Lighting Fixtures:**

There is no restriction on the type, and any light-emitting body can be used as long as its light quality is suitable for the photosynthetic needs of aquatic plants. Sunlights, fluorescent lights, mercury lamps, metal halide lamps, etc., can all be used. Some lighting fixtures will indicate their spectrum, i.e., light quality, while others will not, so be cautious when choosing. As long as the light quality is appropriate, the light intensity should also be suitable; too low or too high will reduce the efficiency of photosynthesis.

**Chlorophyll in Aquatic Plants:**

Chlorophyll in aquatic plants is divided into two types: chlorophyll a and chlorophyll b. In photosynthesis, chlorophyll a directly participates in the photosynthetic reaction, with its absorption peaks located at 430nm in the blue light spectrum and 660nm in the red light spectrum. Chlorophyll b is responsible for transferring absorbed light energy to chlorophyll a, aiding in the photosynthetic reaction and helping chlorophyll a absorb a wider range of the spectrum, with its absorption peaks at 435nm in the blue light and 643nm in the red light. Choosing a light source whose light quality is closest to the needs of chlorophyll a is crucial for the cultivation of aquatic plants. Plant lights are typically manufactured to mimic the spectrum of chlorophyll a, theoretically making them the most suitable.

**Light Compensation Point:**

The light compensation point is the light intensity at which the rate of photosynthesis equals the rate of respiration. Photosynthesis produces sugars, while respiration consumes them. Generally, the higher the light intensity above the light compensation point, the more beneficial it is for the growth of aquatic plants. Different aquatic plants have different light compensation points.

**Calculation of Water Volume:**

The product of the length, width, and height (in centimeters) of the water body divided by 1000 equals the volume of water in liters. Note that when calculating the depth of the water, subtract the part of the substrate; do not calculate from the bottom of the tank.

**General Method for Calculating the Required Light Intensity for an Aquatic Plant Tank:**

Taking fluorescent lamps as an example, the general rule is 0.5 to 1.0W of light intensity per liter of water. For water depths less than 30cm, calculate at 0.5 to 0.6W; for 30 to 40cm, calculate at 0.7 to 0.8W; and for 40 to 50cm, calculate at 0.9 to 1.0W. For water depths greater than 50cm, it is not suitable to use fluorescent lamps and instead, projected light sources should be used. Use the lower standard for green aquatic plants and the higher standard for red aquatic plants. For example, if the dimensions of the water body in an aquatic plant tank are 118cm in length, 48cm in width, and 38cm in height (excluding the substrate and glass thickness), then the volume of water is approximately 215L. With a water depth of 38cm and primarily green aquatic plants, a suitable light intensity would be 150W, calculated at 0.7W per liter.