Plant LED lighting continues to attract attention

Tomatoes, cucumbers, etc. will do well if they get ample water and most importantly, plenty of natural light. But growing plants under artificial light is an interesting new application for LEDs. Once again, these tiny light sources prove that they are definitely not a simple retrofit of halogen and energy-saving lamps. Every LED lighting solution places individual requirements on the product: from cost-effectiveness for consumer applications, high color quality for commercial lighting, to durability for all-weather systems. In this article, we use several examples to illustrate the most important principles to follow in the development of target products.

Cultivating plants under artificial light has long attracted widespread interest, not only because of limited urban space, but also because of the ability to control the conditions under which plants grow. Interest in the horticultural industry has greatly increased due to the discovery that the growth rate of flowers and fruits can be altered according to the light spectrum presented to the plant. Just imagine how many flowers need to be cultivated for Valentine's Day, or imagine the pressure on suppliers to deliver fresh fruit and vegetables to supermarkets by agreed time. Together with the horticultural industry and various universities, OSRAM Opto Semiconductors and other major lighting manufacturers investigated how light affects different plants.

We now know that green plants basically use blue light (around 430 to 490nm) and red light (around 640 to 780nm), mainly for photosynthesis and therefore for energy production, but also with other absorption bands, such as the infrared range around 730nm (see Figure 1), this range controls plant growth and more.

The right mix, coupled with a temporary boost of certain wavelengths tailored to individual plant needs, can trigger the desired effect. LEDs are particularly well suited for this application due to their defined color spectrum and control flexibility. For optimal plant growth, light in the above wavelength range must be provided and does not need to have an overall white appearance. If these parameters are implemented correctly, plants can be grown in closed spaces under artificial light, away from wind and rain.

At the same time, omnidirectional lighting means that plants spend less energy growing vertically, as they would otherwise need to seek sunlight. Instead, they grow more outward and are more productive. Creating a good environment for plants poses a challenge for lamps and LEDs. Due to the high humidity generated by the sprinkler systems used in commercial greenhouses, the LEDs should be exposed to the environment or protected. Chemicals or ash deposits from fertilizer or pesticide contamination may also seep into LED fixtures.

Important parameters for product development: stability and output

Starting from this and other application areas, targeted product development can be carried out according to many details such as lumen package, light quality and package size. LED packages differ fundamentally in two parameters, output level and "stability". The "stability" of LED

components includes not only enhanced reliability, but also the operating temperature and environmental parameters required in a particular application. LEDs with low stability can have very long lifetimes, but only under moderate conditions. More stability almost means more complex, more expensive materials, more complicated processes, and therefore more cost. Therefore, in most cases, parts should be selected based on the stability of the LED for a particular application.

Output level, or the amount of light emitted by each package, is another key factor. Use a large number of LEDs in a single small lumen package in linear or panel luminaires. Applications requiring directional light or even a specific distribution of light will use large lumen packages, better suited as "point sources" for secondary optics. In the middle, there is a range of classic lamps and fixtures that achieve the standardized luminous flux of previous incandescent lamps through a small number of mid-range lumen packages or one large lumen package.

Select the correct LED for the application

Experience has shown that many LEDs optimized for a particular application can also be used very successfully in other areas with little or no modification. In order to define suitable LED packages in all areas of general lighting, a distinction needs to be made in terms of output level and package stability. However, the technological innovations and improvements already established in the LED market cannot be ignored. New application areas such as horticultural lighting are presenting new challenges for product developers to overcome. The above results show that although there are suitable LEDs for almost all established applications, this does not exclude that there may be more suitable LEDs in the future, or that there may be areas that have not been considered so far.