If you look at a vegetable like lettuce, it is a low-light crop. Only 10-12 hours of sunlight is required for the optimum growth of lettuce.
However, for hydroponic lettuce light requirements have to be adequate. If you are growing it indoors or outdoors, you should know how to provide the required lighting conditions.
In this post, I will cover everything you need to know about the lighting requirements for hydroponic lettuce. It will include types of lighting, the amount of lighting, and also I will recommend a few light fixtures that you can use for your hydroponic setup.
I will also touch upon the issue that you can face, which are light related.
Understanding Light Requirements for Hydroponic Lettuce
1. Color
Earlier, I used to rely on sunlight for optimum results. But when I shifted my setup indoors, I realized color played a crucial role in the growth of the lettuce.
In my experience, using red-blue colors from lights positively impacted the lettuce. According to a report published in NCBI, these colors are a major source of photosynthesis in the lettuce.
The studies also show that using the sharp red color of light conditions helps improve the growth rate, and also, the size of the leaves produced is much larger compared to other light conditions.
However, it is the right combination of blue and red that will help you achieve the best results.
You can test out different combinations of red and blue depending on the type of lettuce you plan to grow.
| Light Color | Wavelength Range | Function |
| Blue | 400-500 nm | Promotes vegetative growth, enhances leaf size and color |
| Red | 600-700 nm | Promotes flowering, fruiting, and overall plant growth |
| Green | 500-600 nm | Low photosynthetic effectiveness but helps in the regulation of plant growth and development |
| Far-red | 700-800 nm | Affects plant growth and development by regulating photomorphogenesis |
2. Temperature
Another aspect of light that affect the growth of the lettuce is the temperature of the light.
When growing under the sun, the sunlight produces heat. Similarly, artificial lights tend to produce heat as well.
In the case of the lettuce, the temperature should be between 68 °F and 77 °F. Anything out of this range will affect the growth and yield of the lettuce.
If the lettuce crop is exposed to temperatures lower than 68 °F, it will reduce the ability of roots to absorb water and nutrients from the hydroponic system.
And similarly, if the temperature is above 77 °F, it will force the crop to enter the flowering stage. This can be observed in the form of the curling of leaves.
Not just temperature plays a crucial role in developing taste. If the temperature is high, lettuce tends to be a little bitter.
3. Duration
Lettuce is a low-light crop. Hence, I advise not to expose the lettuce to the full sun. For optimum growth, 10-12 hours of sunlight is more than enough.
Exposing it to more than that will cause bolting and make the lettuce bitter.
However, the amount of light it requires depends on different facts like growth stage, variety, and stage of growth.
So make sure you provide adequate sunlight for every growth stage. You can follow this table to get some idea:
| Growth Stage | Light Required |
| Germination | 12-16 |
| Seedling | 12-16 |
| Vegetative | 10-12 |
| Heading | 10-12 |
| Bolting | 8-10 |
Also, Take Look At Our Top Hydroponic System For Lettuce
Types of Light for Hydroponic Lettuce
Another question that is natural for any grower is which light is good? Natural or Artificial?
I will provide you comparison so that you can decide which is good for our setup.
1. Natural light
We know everything grows in sunlight because it has all the essential elements needed for plants to grow. But let’s see the pros and cons in terms of growing lettuce.
| Pros | cons |
| It provides a full light spectrum, which includes much talked about red and blue light. | Not a reliable source of light. Especially in winter or monsoons. |
| In the right conditions, it is also the main source of heat for plants. | No control over it if you want restricted light for low-light crops like lettuce. |
| It is free for life which is important for commercial setups. |
2. Artificial light
If you want to grow lettuce year around, there is no better option than artificial light. You have complete control over the light, and also the location of the crop is not dependent on the lighting conditions in your area. Let’s see the pros and cons of using it.
| Pros | Cons |
| Suitable for year around crops. | It is not free. Energy bills may be a major cost of growing lettuce in these lights. |
| More control over the lighting conditions. | Maintenance needed. |
| Location is not light dependent. | Limited life. |
| Suitable for more commercial set-ups. |
How to Provide Adequate Light for Hydroponic Lettuce?
Once you have understood the types of lighting requirements for hydroponic lettuce, you need to apply them to your setup.
For these, you can follow my simple three-step setup.
1. Choosing the right light fixtures
When choosing lights for the hydroponic setup, you have the option of LEDs, HID, and fluorescent lights. Most gardeners prefer using LEDs, as they offer a range spectrum. Also, you can use the same light for other crops as well.
I suggest trying to find some good quality white LED lights or Red-Blue LED lights with a dimmer switch.
And if you want to automate your setup, you can get lights with a timer.
2. Proper placement of light fixtures
I have already established you have to provide exactly what the crop requires. You must ensure this rule is followed when hanging the lights over the lettuce.
Each type of light has different power, so they have to be hung at a different distance from the lettuce.
When we compare the three most popular types of lights for growing leafy vegetables in a hydroponic system, LED lights have to be hung higher compared to other types of lights. And fluorescent lights need to be closer to the lights for the best effect.
Follow this table for the best idea. I have categorized it based on the power of the light and the corresponding distance required for it.
| Light | Power (watt) | Distance From Plant |
| HID | 400 W | 20 inches |
| 1000 W | 30 inches | |
| LED | Upto 400 W | 16-20 inches |
| 400-500 W | 20-24 inches | |
| 500-800 W | 24-26 inches | |
| More than 800 W | 26-42 inches | |
| Fluorescent | Average powered | 5-12 inches |
3. Scheduling the lighting for optimal growth
Apart from controlling the intensity of the light you have to control the duration for which the light remains on.
A dedicated lighting schedule for each crop you grow in a hydroponic system is useful.
It can be done either manually or by using automation with the help of grow light controllers.
With the help of controllers, you can set the switch on/off schedule for lights.
For lettuce, you need to keep the lights on for 10-12 hours and off for the rest of the day. However, the schedule will vary for different types of lettuce.
Conclusion
Each variety has different light requirements, so make sure you find out what hydroponic lettuce light requirements are for the type you are growing. By following my suggestions, you will have a fair idea about it.