An earlier white paper titled “Seasonal Variation in Natural Light” discusses in detail how sunlight changes both seasonally and daily in terms of both intensity and spectra. To recap, the major factors that contribute for variation in natural light over the course of a day or a year are solar elevation angle – i.e., how high the sun is in the sky and the resulting angle of incident sunlight on the Earth’s surface – and atmospheric composition which results in differential scattering of light by particles in the atmosphere (Seguin, 2022). Without spectral compensation, a smart lighting solution’s only manner of response to a cloudy day, for instance, would be to increase lighting intensity – thus consuming more electricity overall. However, the relationship between weather and natural light is complex and cannot be addressed by considering brightness alone.

Researchers Chiang et al., (2019) conducted an in-depth study that tracked all the spectral changes of natural light at a mid-latitudinal location over the course of an entire year. Their findings highlight the significant impacts of atmospheric weather events on the natural light available to plants and how weather and climate factors interact to further complicate light patterns. In a general sense, from sunrise to sunset, the researchers observed that blue light (400 – 500 nm) will decrease as the day progresses and green (500 – 600 nm), red (600 – 700 nm) and far-red (700 – 780 nm) wavelengths will increase (figure 1.)

They found that the solar elevation angle and weather events together had compounding effects. For instance, at low solar elevation angles – i.e., during sunrise or sunset – the red to far-red light ratio maybe 0.8 on a cloudy day and 1.3 during clear sky conditions. At solar elevation angles lower than 20°, atmospheric weather conditions will strongly impact available red and blue wavelengths in the light spectra such that a significantly higher proportion of red light and a lower proportion of blue light will result. During mid-day – at higher solar elevation angles – the opposite trend was observed but to a lesser degree with the proportion of blue light increasing marginally with increasing cloud cover, and the proportion of red light decreasing marginally.

A truly dynamic lighting solution – like that of Sollum Technologies’ – can address weather variation by adjusting light spectra as well as light intensity in immediate response to changes in ambient light. For other smart lighting systems, mimicking clear sky conditions on a cloudy day can only be attempted by increasing brightness – thus consuming additional electricity that may not be necessary. Precise sunlight compensation fine-tuning both the spectrum and intensity leads to energy savings.

The following graphic provides an example of dynamic compensation as accomplished by one of Sollum Technologies’ smart LED grow light. In this example, the following light recipe is precisely and accurately maintained thanks to dynamic compensation: LED lights turn on early in the morning – before sunrise – and recreate the full sunlight spectrum including far-red (the grower may choose to include far-red for several reasons such as to promote shoot elongation during vegetative growth in crops). As the Sun rises, not only is more photosynthetically active radiation (PAR) available to the plants, but more far-red light is available as well, and the ratio of blue to red light decreases. Responding in real time, the intensity of the LED lights is reduced, far-red is deactivated and the fixture’s blue:red wavelength ratio output is increased. As the Sun sets, the intensity of the LEDs rises, the spectrum shifts accordingly and far-red is reactivated. This is only one possible light recipe out of an infinite number that may be employed using Sollum Technologies’ smart LED grow light solution.

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Precise sunlight compensation fine-tuning both the spectrum‍and intensity components leads to energy savings.

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