INTRODUCTION
The DLI meter calculates daily light integral (DLI) and photoperiod. DLI refers to the total amount of PAR or ePAR
incident on a plant in a 24-hour period, expressed in units of moles per square meter per day (mol m
-2
d
-1
).
Photoperiod is the total amount of time in which PAR or ePAR is incident on a plant during a 24-hour period and is
expressed in units of hours (h). Both DLI and photoperiod influence plant growth and development, and they are
often measured in greenhouses and growth chambers to aid in light management and decision making.
Apogee Instruments DLI meters consist of a cast acrylic diffuser (filter), interference filter, photodiode, signal
processing circuitry, and an LCD display mounted in an ASA plastic housing. DLI meters are designed for single or
continuous measurements of PPFD or ePPFD; DLI; and photoperiod. The DLI meter uses a USB-C cable (included
with the meter) to download the stored data as a CSV file to a computer.
PAR vs ePAR
Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is traditionally defined
as total radiation across a wavelength range of 400 to 700 nm. However, additional research has indicated that
photons outside of this range contribute to photosynthesis as well (Hogewoning et al., 2012; Murakami et al.,
2018; Zhen and van Iersel, 2017; Zhen et al., 2019). Research has shown that far-red photons, wavelength range
from 700 to 750 nm, work synergistically with photons in the traditional PAR range, but alone are inefficient at
driving photosynthesis (Zhen and Bugbee, 2020a; Zhen and Bugbee, 2020b). As a result, an extended PAR (ePAR)
definition has been proposed across a range of 400 to 750 nm (Zhen et al. 2021). Apogee DLI meters are designed
to measure either PAR (models DLI-400 and DLI-500) or ePAR (model DLI-600). The DLI-400 and DLI-500 both
measure PAR, however, the DLI-500 is accurate under all light sources, while the DLI-400 is a low-cost option that
is accurate under sunlight and broadband light sources only. PAR and ePAR are often expressed as photosynthetic
photon flux density (PPFD) and extended photosynthetic photon flux density (ePPFD), respectively, in units of
micromoles per square meter per second (µmol m
-2
s
-1
).
Hogewoning et al. 2012. Photosynthetic Quantum Yield Dynamics: From Photosystems to Leaves. The Plant Cell, 24: 1921
–
1935.
Murakami et al. 2018. A Mathematical Model of Photosynthetic Electron Transport in Response to the Light Spectrum Based on Excitation
Energy Distributed to Photosystems. Plant Cell Physiology. 59(8): 1643
–
1651.
Zhen et al. 2019. Far-red light enhances photochemical efficiency in a wavelength-dependent manner. Physiologia Plantarum. 167(1):21-33.
Zhen and Bugbee. 2020a. Far-red photons have equivalent efficiency to traditional photosynthetic photons: Implications for redefining
photosynthetically active radiation.
Plant Cell and Environment
. 2020; 1
–
14.
Zhen and Bugbee. 2020b. Substituting Far-Red for Traditionally Defined Photosynthetic Photons Results in Equal Canopy Quantum Yield for CO
2
Fixation and Increased Photon Capture During Long-Term Studies: Implications for Re-Defining PAR.
Frontiers in Plant Science.
11:1-14.
Zhen and van Iersel. 2017. Far-red light is needed for efficient photochemistry and photosynthesis. Journal of Plant Physiology. 209: 115
–
122.
Zhen S, van Iersel M and Bugbee B (2021) Why Far-Red Photons Should Be Included in the Definition of Photosynthetic Photons and the
Measurement of Horticultural Fixture Efficacy. Front. Plant Sci. 12:693445. doi: 10.3389/fpls.2021.693445
Содержание DLI-400
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