“Hybrid lighting is not about replacing LEDs, it is about using sunlight as a controllable resource indoors”

Prof. Längle, indoor farming promises efficiency and resilience, yet lighting remains a major bottleneck. Why?

Thomas Längle: Lighting drives both electricity demand and heat load. In FutureProteins, a Fraunhofer flagship project on closed cultivation systems for alternative protein sources, we explored hybrid lighting to make indoor plant production more efficient than artificial light alone. Even modern LEDs still convert the major part of the supplied electrical energy into heat, and that heat must be removed to keep the cultivation environment stable. Lighting therefore consumes energy twice: directly for illumination and indirectly for cooling.

What does “hybrid lighting” mean in this context?

It is more than simply adding daylight to LEDs. Our system collects sunlight over a larger area, guides it into a compact optical path, separates it spectrally, transports it through fibre bundles, and mixes it with artificial light in a controlled way. A key advantage is that infrared radiation can be removed before the light enters the indoor system. This makes it possible to use the visible part of sunlight while keeping much of the unwanted thermal load out − or redirecting it to other purposes.

What has Fraunhofer IOSB demonstrated in practice?

The project delivered a working proof of concept. Fraunhofer IOSB developed and integrated a hybrid lighting system including sunlight collection, fibre coupling, light transport, mixing, spectrometric monitoring, and control of the spectral composition. It also enables light recipes, meaning the spectral mix can be adapted to specific needs. At the same time, FutureProteins and related work showed that, while clearly superior in terms of physical efficiency, hybrid lighting does not automatically pay off economically under current conditions.

So beyond vertical farming, where do you see potential?

Wherever high-quality indoor lighting is needed but conventional daylight access is limited − or where daylight brings too much heat into the building. That includes factory halls, office buildings, museums, and windowless retail areas. In such settings, hybrid lighting could help reduce dependence on purely artificial illumination while improving light quality and easing the cooling burden that usually comes with large glazed areas or high lighting loads. Sunlight offers a full-spectrum white light that artificial systems do not reproduce in the same way. Hybrid lighting opens up a new option: using daylight indoors while decoupling illumination from thermal load. That is why the idea matters not only for agriculture, but for indoor environments more broadly.

Thomas Längle is the spokesperson for the Advanced Sensing business unit and head of the Visual Inspection Systems (SPR) department.