Lighting Strategies: Daily light integral (DLI) with and without far-red for lettuce

Objective of the experiment: To understand on how different light intensities that sum up to equal DLI is effecting growth of lettuce. Earlier trials without far-red had showed similar results when aspect of crop production between the different ways to distribute the light over a day.

Place and duration: Heliospectra PlantLab
Species:  Lettuce – Black seeded Simpson
LampsLX601C
PAR: Varies to achieve DLI of 13.0
Photoperiod: 16 hours (8.00-0.00)
Results: The lettuce grown with far-red were larger and had higher biomass than lettuce grown without far-red.
Objective of the experiment: To understand on how different light intensities that sum up to equal DLI is effecting growth of lettuce. Earlier trials without far-red had showed similar results when aspect of crop production between the different ways to distribute the light over a day.

 

METHOD

Lettuce, Black seeded Simpson, were sown (4 seeds per pot) and kept in the germination area under 24 hours light for 5 days. The pots were thinned out to 1 plant per pot and placed in growth units, a 1.4-m2 (15ft2) open area with reflective curtains with a LX601C.

The photoperiod for all units were 16 hours, 8.00 – 0.00. The room temperature set point was 22ºC/17ºC (day/night) and humidity set to 60 %.

The LX601C was used to set DLI light strategies in the experiment with the same spectrum within PAR. The light intensity varied over the day to simulate natural daylight intensities; lower morning and night while highest during mid-day. Two spectrums were tested. The first spectrum contained blue, red and white LEDs. The second day simulation contained additional far-red added to the spectrum with a constant on red: far-red. Both light treatments sum up to the same daily light integral, DLI = 13.

28 days into the experiment, 5 pots per unit containing 1 plant were collected and measured. Average plant height, head size and leaves were counted, and fresh weight taken with a scale.

RESULTS

The lettuce grown under a spectrum without far-red were smaller, more compact and darker green than with far-red. The visual difference between the treatments was that with far-red the lettuce were larger, looser and paler in color. A 13% increase in the diameter of the lettuce were recorded in comparison to lettuce treated with light containing no far-red. It also had a 43% increase in fresh biomass, compared to lettuce grown under the day simulation without far-red.

Daily light integral with and without far-red for lettuce

Image: Simpson lettuce at harvest, 28 days of treatment, from left to right without Far red and with Far red

This is a summary of the findings produced by the Heliospectra's PlanLab. For the full report please contact our lab or sales team here