Never the less supplemental lighting from HPS SON-T lamps do have a positive effect mainly related to the heat radiation of the lamps increasing the leaf temperature and as a result promoting extra photosynthesis.
Typical sunlight spectrum in winter time at Western Europe – 2PM.
In general the supplemental light levels during day time should be obtained from the LED grow lights (and preferable in this way that the LED grow light interacts with a PAR meter at canopy level) what saves the most of your energy. For daylight extension the LED grow lights stay on while extra HPS SON-T lamps promote the extra photosynthesis (but at lower energy level as lighting with just SON-T).
A perfect LED spectrum for this balanced growth system is retrieved from the CoolGrow® 3REQWFR, resulting in strong glossy plants and a tremendous energy saving because of the very triggered spectrum without energy losses at non-needed wavelengths.
Keep in mind far red levels should stay under 7% to avoid too much stem elongation as it also trigger the “shade escape effect”.