Grow lights – What is the right lighting for plants?
Grow lights promote the growth of plants and help them to overwinter. Suitable light sources can be used instead of, or in addition to, natural daylight. It's important to pay attention to the distribution of the light spectrum. Red and blue light promotes photosynthesis, growth and the development of flowers and fruits. The type of grow light is also important: the light source must have sufficient illuminance (lux) but not generate so much heat that it damages the plants.
What are grow lights?
Grow lights are lamps that imitate the light spectrum of natural sunlight. This can promote plant growth or make it easier for plants to overwinter when there is less daylight.
Which grow light is the best?
The ideal plant lighting for growing and overwintering contains a high level of blue in the light, but a certain level of red is also needed to promote correct plant growth. Grow lights should be as similar as possible to sunlight, so lamps with the colour daylight white are particularly recommended. Lamps with 1A or 1B in their specifications can also be used as grow lights.
There are also lamps that are specially designed for optimal plant growth, such as the Sylvania GroLux T8 tube. This fluorescent tube has a colour temperature of 8,500 Kelvin which promotes plant growth. Please note that the Sylvania GroLux plant lamp is intended for use in greenhouses and conservatories and is not suitable for use in private households. It's also ideal as lighting for freshwater aquariums because it brings out the natural colours of fish and aquatic plants.
LEDs as grow lights
Whether it's LED bulbs or LED tubes, modern light-emitting diodes are ideal for plant lighting. Make sure to choose the right colour temperature for the plants you want to illuminate. Although LEDs are slightly more expensive to buy than conventional light sources, they make up for this in a short space of time thanks to their extremely low energy consumption. With a recommended lighting time of up to 15 hours per day (see table below), LED plant lamps are definitely worthwhile.
Fluorescent tubes as grow lights
Fluorescent tubes are also available in the colour daylight white. Because the heat dispersion is relatively low, it's possible to place fluorescent tubes at a distance of 20-30 cm from the plant. Fluorescent tubes that are placed further any further away disperse their light over a greater area and do not achieve the required illuminance (lux). In addition, in contrast to LEDs, fluorescent tubes consume considerably more energy and have a much shorter life span.
Gas discharge lamps as grow lights
Gas discharge lamps are regarded as a particularly good solution for illuminating plants. Different types that exist are commonly abbreviated with the letters HPS, NAV and SON. Although they do not provide the ideal light spectrum as grow lights, they score points for their particularly high luminosity: gas discharge lamps reach wattages of 1,000 W and are, therefore, particularly bright. The lamps also produce a lot of heat, which is why a greater distance to the plants is recommended. Another disadvantage is that gas discharge lamps are expensive to purchase and also have very high running costs due to their high energy consumption. For this reason, the use of these products is usually limited to professional growers who illuminate their plants all year round. It is not worth purchasing gas discharge lamps purely for overwintering plants in a private space.
Energy saving lamps as grow lights
Due to their low heat generation, daylight white energy-saving lamps (also known as CFL) are also perfectly suitable for plant lighting. Their compact design makes them ideal as light sources for individual plants.
Incandescent lamps as grow lights
Incandescent lamps are not suitable for lighting plants. They have a high amount of red in their light, usually between 2,300 and 2,500 Kelvin and, therefore, have an extra warm white colour temperature. Although plants need red light to grow, too much of it is unhealthy: excessive red light leads to enormous, unhealthy growth and a collapse of the plant under its own weight. In addition, incandescent lamps generate an extremely high level of heat. This also damages the plants.
Conclusion: LED lamps as optimal grow lights
Without question, LED lamps offer the best combination of ideal plant light and energy-saving lighting. Sodium vapour lamps, which can fully reproduce sunlight, are also ideally suited. Due to their high purchase and operating costs, however, they are only really useful for professional applications. Special plant lamps such as the Sylvania GroLux are also particularly recommended for greenhouses.
Why should I use a grow light?
Plants need sufficient light to carry out photosynthesis. Without photosynthesis the plant dies. If plants are placed in rooms with little light or in dark corners, they often do not get enough daylight. And even in winter, when you bring in your plants for overwintering, you should provide additional lighting. This is because plants do not feel comfortable in heated rooms and there is rarely sufficient sunlight in cellars or storage rooms. Additional plant light is, therefore, essential for the optimal storage of your plants indoors. Even if you want to help seedlings grow, or if you want to start growing certain vegetables earlier, you are well advised to provide additional plant lighting.
How do grow lights work?
Grow lights imitate natural sunlight, which provides a colour spectrum between 5,000 and 10,000 Kelvin: this light colour is also called daylight white. The colour spectrum of natural light is composed of green, red and a high proportion of blue. The green part of the light is not needed by plants and is therefore reflected - this is why they have their green colour. Plants, on the other hand, use blue and red light. The right mix between the proportions in the light is crucial. Too little intense light or too little red will result in unattractive growth with pale shoots and few leaves. The red colour spectrum promotes the growth of fruits and flowers, while the blue one helps the plant itself to grow.
How long must I leave the grow light on?
For optimum lighting, the illuminance is paramount. Illuminance is measured in units called lux (lx). Depending on the plant, the recommendation for the lux value and how long the lighting needs to be on may vary. As a general rule, you can use the following table as a guide.
|Type of plant||Lux||Lighting duration|
|Plants in moderate zones||700 lx||9 hrs|
|Subtropical plants||1.000-2.500 lx||12-15 hrs|
|Tropical plants||1.500-5.000 lx||12-15 hrs|
Where do I place my grow light?
Artificial growing lights should illuminate plants from above, like sunlight does. The further away the lamp is from the plant, the lower the light intensity (lux). As a general rule, a distance of 30-40 cm between the plant crown and the light source is recommended.