Thermal management for high-performance LED lamps in greenhouse lighting systems

The efficiency of LED lighting is improving from generation to generation. Nevertheless, high-power LEDs still develop considerable power losses. Blue and red LEDs are still the most efficient. Here, more than 50% of the electrical energy used is converted into light photons.

White LEDs, which are often used in lighting to create a natural light impression, use special dyes. This converts the light from red and blue diodes into green and yellow light. This transformation consumes energy, so that such LEDs usually only have an efficiency of around 30-35%. This means that 65-70% of the energy used is lost as heat .

The service life, colour fidelity and brightness of LEDs are very directly linked to the operating temperature. For high-quality and long-lasting LED products, it is therefore important to ensure that the temperature of the light-emitting surface is as low as possible.

Simple LED luminaires, which often only use an extruded aluminum profile without good coupling of the LEDs to cooling surfaces, often have a service life of less than 25,000 hours. 

If longer power-on times are planned or trouble-free operation over many years is desired, there is no getting around thermal management. Well-known systems such as heat sinks, heat pipes, heat conducting pastes and heat conducting films have been used successfully for many years in electronic devices such as laptops or tablet PCs. These technologies are also ideally suited to making high-quality LED lighting durable. Operating times of up to 75,000 hours can realistically be achieved in this way.

Compared to other types of lighting, LEDs also produce significantly less infrared radiation. In greenhouse construction, this means that the lamps can be installed significantly closer to the plants than high-pressure sodium vapor lamps or halogen lamps. As the light intensity decreases with the square of the distance, more plant-effective light can be introduced into crops in this way. In addition to improved plant growth rates, this significantly reduces energy consumption compared to traditional lighting methods.

However, heat management is also necessary in the constant current sources (ballasts for LEDs, also known as LED drivers). The transformation of the available voltage (120-400 VAC) also generates power loss at LED outputs of 100-1000 W, which must be reliably dissipated by the electronic power components. Due to the high voltage, galvanic isolation (electrical insulation) is often an important part of the thermal path.

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