DLI-400: Daily Light Integral and Photoperiod Meter (Sunlight Only)

Apogee Instruments

DLI-400: Daily Light Integral and Photoperiod Meter (Sunlight Only)

  • Vendor:Apogee

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Buy 1 $444.00 ea
Buy 10 $421.80 ea

Apogee's new DLI-400 meter is designed to measure photosynthetically active radiation (PAR) 400–700 nm and is a low-cost option that is accurate under sunlight and some broadband light sources only. Post-measurement correction factors can be applied to improve accuracy under light sources; click here for more information. In addition to measuring PAR, the DLI-400 meter calculates daily light integral (DLI) and photoperiod. DLI refers to the total amount of PAR or extended PAR (ePAR) incident on a plane 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 plane 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. 


The DLI-400 meter has two different screen modes: stored data and live view data. In the stored data screen, it shows the DLI measurement, photoperiod, and which day the data was collected (up to 99 days ago). The live view data screen displays a running average of PPFD from the last 2.5 seconds.


The DLI meters consist of a cast acrylic diffuser (filter), optical 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.

Calibration Uncertainty
± 5 %


Measurement Repeatability
Less than 0.5 %


Measurement Range
0 to 4000 µmol mˉ² sˉ¹


Long-term Drift
Less than 2 % per year


Field of View


Spectral Measurement Range(± 5 nm)
370 to 650 nm (sunlight only)


Directional (Cosine) Response
± 5 % at 75˚ zenith angle


Temperature Response
-0.04 % per C


Response Time
2.5 seconds


Measurement Frequency
3 minutes


Data Log Capacity
99 days (DLI & Photoperiod), 10 days (30 min PPFD/ePPFD averages)


Less than 1 % (up to 4000 µmol mˉ² sˉ¹)


Stored Data Resolution (PPFD)
0.1 µmol mˉ² sˉ¹ (when ≥ 1000, the screen will not display the decimal)


Stored Data Resolution (DLI)
0.1 mol mˉ² dayˉ¹


Stored Data Resolution (Photoperiod)
0.1 hours


CSV file via USB-C data transfer


ADC Resolution
24 bits


Operating Environment
-10 to 60 C; 0 to 100 % relative humidity


Ingress Protection


Mounting Compatibility
Brass 1/4-20 threaded mount


Battery Life
Approximately 6 months


1.91 W x 2.31 H x 0.93 D (inches)


67 g


4 years against defects in materials and workmanship


Made in the USA