DLI & Photoperiod Display Sensor

R8 500 - R12 660


Apogee’s new, rugged DLI meters make it easier than ever to make research-grade measurements of PPFD, daily light integral, and photoperiod at any location.

The different meter models can take instantaneous readings of PAR or ePAR (Extended PAR - beyond the traditional 400–700 nm range) and automatically record the daily light integral (total photons in mols) and hours of light (photoperiod in 0.1 hours) for up to 99 days. This data can be viewed on the screen by toggling through the screens or downloading via USB cable.

Compared with the ePAR and PAR-FAR sensors, the DLI Meter is more affordable and easier to use because it is a standalone product that displays all its readings and history of the data on the digital display. Recommend for people who want an easy solution to view and understand light data.

    Three Models

    • DLI-400: Lowest-cost option is accurate for measuring 370-650 nm in sunlight and under some broadband light sources.
      • Specially calibrated for sunlight
    • DLI-500: Full-spectrum is accurate for measuring 389-692 nm under all light sources.
    • DLI-600: ePAR is accurate for measuring the new ePAR 383-757 nm range under all light sources. We recommend this unit.


    Data Collection and Display

    • Meter displays real-time PPFD/PAR or ePAR in µmol m-2 s-1; daily light integral (DLI) in mol·m-2·d-1; and photoperiod in 0.1 hour increments.
    • DLI and photoperiod measurements are recorded continually every three minutes with a darkness threshold of .1 µmols.
    • Daily data is stored up to 99 days and displayed onscreen by toggling through the screens.
    • DLI, photoperiod, and 30 minute PPFD averages can be downloaded as CSV files via the USB-C port under the battery cover using the included USB-A to USB-C cable.

    240w regular ppfd

    What is DLI?

    Daily Light Integral (DLI) is the total number of photosynthetically active radiation (PAR) photons (traditionally those between 400-700 nm and now 400-750nm) incident on an area over the course of a day.
    DLI is a function of both the intensity and duration of the photosynthetic light falling on the target over a day and is most commonly expressed as moles of light per square meter per day or mol m-2 d-1.

    Benefits of knowing DLI?

    Specific plants and other photosynthetic organisms, like corals, require different daily light integral levels to achieve optimum growth. There are many resources available that list different DLI recommendations. 
    To make an accurate measurement of the DLI during a day with changing light levels, a high-quality quantum sensor must be used and coupled with a data recorder to log and sum all the measurements from the day. A quantum sensor, also known as a PAR or PPFD (photosynthetic photon flux density) sensor, measures the intensity of photosynthetic light incident on a target.

    Almost universally, photosynthetic light is defined as equal weighting of all photons between 400-700 nm (DLI-500). Newer research is showing that photons between 400-750 nm (DLI-600) are also photosynthetic and should be counted towards DLI.

    DLI for cannabis

    Different strains have different DLI stress points, and while the range is wide, virtually all strains can handle somewhere between 40-50 DLI.

    If your light cannot metabolize the current light, you will experience light stress because if an absorbed photon does not get absorbed, it creates heat in the plant and that heat can cause stress.

    While a plant can only grow as fast as the weakest link, the primary driver of plant metabolism is light. Careful testing and logging will allow you to optimize your DLI targets.

    If light-stress is seen below 45 DLI, the grower should investigate ways to improve their nutrient throughput, environmental conditions and so on - to be able match the metabolism demanded, or dial the DLI target back.

    The Importance of DLI in Greenhouse Production

    DLI in green house production is critical to be able to adjust your supplemental lighting.

    As for the energy consumption with these higher levels of supplementation, in general the value of cannabis yield exceeds the cost of the electricity required to produce it by 20+ times. So, electrical consumption is just not an important consideration compared with the yield results. Only if the necessary power infrastructure is unavailable, or if the budget is not feasible should lower supplemental levels be chosen.  At current prices, cannabis always justifies the electricity necessary to produce it up to the DLI limit.

    To determine DLI of an area illuminated by a light source with a constant output and known duration, an instantaneous PAR measurement can be made and used to calculate DLI
    Calculation of DLI from an instantaneous PAR measurement relies on the assumption that the light source is constant while it is on. If there is variability in the light source, such as a greenhouse, then calculation of DLI from an instantaneous PAR measurement will be incorrect.

    Application of use:

    • PPFD
    • DLI
    • Photoperiod
    • Data Recording
    • Canopy Light Absorption
    • Greenhouse Light Absorption of Windows / Outdoor Netting
    • Adjust Supplemental Lighting



    Accurate, Stable Measurements

    Meters are cosine-corrected to maintain accuracy when radiation comes from low angles (± 5 % at 75° zenith angle). Long-term non-stability determined from multiple sensors in accelerated aging test and field conditions is less than 2% per year.

    Rugged Design

    Housing is built tough to withstand harsh environments and is dustproof and waterproof up to IP65. Unit consists of a cast acrylic diffuser (filter), optical filter, photodiode, signal processing circuitry, LCD display, and two AAA batteries (included). Battery lasts +- 6 months.


    Unit can be placed directly on any flat, level surfaces or mounted by attaching to commonly available camera tripods, clamps or stakes using the standard camera-sized ¼-20 threaded port in the bottom of the unit. A small plastic soil stake is included for standing the unit in turf or other soft soils.

    Typical Applications

    Monitoring PAR or ePAR intensities, daily light integral, and the photoperiod of grow-lighting is critical for plant health, growth rate, photosynthesis levels, plant morphology, and crop steering. Required levels vary greatly by species and should be measured and controlled for optimum specimen health.


    To ensure accuracy, each DLI meter is carefully calibrated in controlled conditions and traceable to NIST reference standards.


    All Apogee products are backed by an industry-leading 4-year warranty.

    How to use

    1. Find out the DLI requirement of your crop.

      • Cannabis flowering 20-65 DLI

      2. Obtain lighting that provides you the maximum DLI of the crop you plan to grow.

      • Cannabis max 45 DLI in flowering to optimize most strains
      • Some strains can go up to 65DLI

      What ppfd am I aiming for?

      Cannabis Stage Recommended PPFD range (μmol s-1 m-2 )

      • Seed Sprouting / Root Cloning: 100 to 400
      • Vegetative Growth: 250 to 600
      • Flowering (Reproductive) Stage: 600(26 DLI) to 1000 (43 DLI) without co2
      • Flowering (Reproductive) Stage: 1000(43 DLI) to 1500 (65 DLI)+ with co2

      What DLI am I aiming for?

      Cannabis recommended flowering 20-65 DLI - will have a uniform increase in yield proportional to DLI right up to 45 DLI, with many strains going as high as 50 DLI or more. For vegetative stage the DLI should not be less than 25% of the flowering DLI to avoid potential "light" shock.

      We’ve noticed that different cultivars respond differently to light intensities. Some may reach a light saturation point a lot faster than others.

      "At one of our farms, I had a Panama Red variety that would not produce anything if I moved my light level over about 900 PPFD(DLI 38.88 at 12 hours of light). No matter how much extra CO2 I gave it, no matter how much extra water and mineral nutrients I gave it, that plant peaked out when I gave it a treatment of 900 PPFD of light. What that told me is that the genetic limitation might have been reached right there, and therefore every plant has a genetic limitation." 


      Product Demo and informational Video


      Green Houston is an  official  distributor for all Apogee instruments in Africa, imported directly from Apogee USA.

      Please contact office@greenhouston.co.za for all Apogee sensors and variants.

      Please note: Apogee products are imported from the USA and due to the fluctuating exchange rate, prices are not fixed and may be subject to change. Requesting a quote before placing an order is highly recommended.