一, The basics of photobiology: how plants "see" LED light
Plants can see light because of the combined effects of the photosynthetic pigment system and photosensitive pigments. Chlorophyll a/b absorbs light best at 660nm red and 450nm blue, while carotenoids help out at 480nm blue. This natural spectral selectivity lets LED technology affect plant growth by carefully changing the spectrum components.
The spectrum of regular LED lights (white LED) is made for human eyesight, but it still has blue light (450–470nm) and red light (620–660nm) that plants need to photosynthesise. Studies indicate that approximately 18% to 25% of the photon flux emitted by white LEDs falls within the efficient photosynthetic radiation spectrum for plants (400-700nm). This percentage is lower than the 80% to 90% of professional plant lamps, yet it can still cover the minimum needs for extra light. For instance, when it rains or when there isn't much light inside, regular LED lights can keep plants exposed to light for 14 to 16 hours a day. This shortens the life cycle of green foods like lettuce by 15% to 20%.
二, Application scenario: The range of typical LED lights
1. Short-term more light and plants with leaves
For plants with leaves, such jackfruit and chlorophytum comosum, regular LED lights can be utilised as short-term light sources. Experiments have demonstrated that irradiating plants for 6 hours a day from a distance of 30 cm can raise the chlorophyll content of their leaves by 12% to 15%. But using it for a long time (more than three months) could make the stems too long, and you would need to trim them regularly.
2. Growing seedlings and herbaceous plants
When making herbaceous plants like sprouts and herbs in a factory, regular LED lights and reflective film can use 80% of the light energy. A family farm in Shenzhen used a modified LED ceiling light (PPFD value of roughly 120 μ mol/m ²/s), which raised the rooting rate of basil seedlings from 65% in natural light to 92%. But the rate at which fruit crops (like tomatoes) set fruit only went up by 8%, which is a lot less than the 35% increase that professional plant lighting caused.
3. Emergency lighting throughout the seasons
In the winter, regular LED lights can be used to light greenhouses in northern areas. Tests at a vegetable base in Hebei Province have shown that adding regular LED lights for 4 hours a day, even when the weather is very bad and there is less than 4 hours of light, can keep 78% of the normal cucumber yield. However, the vitamin C content of the fruit is 19% lower than that of the professional supplementary lighting group.
三,Technical problems: Three main problems with regular LED lights
1. Unbalanced spectral parts
Green light (500–570 nm) makes up 40% to 50% of regular LED lights, yet plants only absorb less than 5% of it. This "ineffective light" not only makes light energy less useful, but it can also raise the temperature of the leaves by 2 to 3 degrees Celsius through thermal effects. To fix this, the lamp spacing should be increased (40 to 50 cm is best).
2. Not enough light intensity
Professional plant lights can have a PPFD value of 600–1000 μ mol/m ²/s, while regular LED lights only have a PPFD value of 80–150 μ mol/m ²/s at a distance of 30 cm. For crops that need a lot of light to thrive (like chilli peppers), regular LED lights need to stay on for more than 12 hours to provide the same effect as professional lights for 6 hours. This uses 2.3 times more energy than professional lights.
3. No dynamic regulation
For plants to grow, the quality of the light needs to change between the vegetative growth stage (when 60% blue light is needed) and the reproductive growth period (when 70% red light is needed). Normal LED lights have a fixed spectrum and can't change the quality of the light dynamically like professional lights can. This causes "light quality discomfort" in crops like tomatoes, which means weak stems during the nutritional growth period and not enough flower bud differentiation during the reproductive growth period.
四,Optimisation Plan: A plan to make regular LED lights work better
1. Technology for changing the spectrum
Some green light can be changed into red light by putting fluorescent powder on the surface of LED beads. There are already kits on the market that can change regular LED lights such that they have 15% to 30% more red light and 18% more photosynthetic efficiency. For instance, when growing succulent plants, the customised LED lights can make the plants 25% more compact and the leaves 12% thicker.
2. Putting together a reflection system
When used with aluminium foil reflectors or diffuse reflective coatings, the light energy utilisation rate can go up from 35% to 58%. A home lab test in Hangzhou found that after utilising a reflecting system in a 1 ㎡ planting area, the extra light from regular LED lights is only 68% as good as that from professional lights, but they cost only 1/5 as much.
3. Smart control module
An external photosensitive sensor and timer can automatically change the amount of light and the time. For instance, if the ambient light level is less than 2000lux, the system automatically turns on the LED fill light for the given amount of time to avoid light suppression from too much light.
五, Market Trend: How Regular LED Lights Are Changing
As plant factories move into homes, the "plant-based" change of regular LED lights has become a new fad. In 2024, businesses like Xiaomi and Philips will release "full spectrum LED bulbs." These bulbs use multi-chip combination technology to span the entire 400-700nm range, have a PPFD value of 200 μ mol/m ²/s, and cost 60% less than professional lights. This kind of product makes up 32% of the market for balcony gardening, and by 2025, it is predicted to make up more than 50%.
At the same time, modular design has become an important new idea. IKEA's "Plant Growth Light Bar" can be easily added to current LED lamps. You can change the spectrum and brightness of the light with a mobile app, turning regular lamps into "smart plant lights" right away. This "lightweight transformation" approach is making it easier for people to start home plant companies.
