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Apogee Instruments, a renowned manufacturer of scientific-grade quantum PAR meters, recently released its new product line of daily light integral (DLI) meters. All three models measure PPFD, DLI, and the photoperiod. The DLI meters are able to record and store the data for 99 days. Within this article, we want to take a look at these new products in the lens of a cannabis grower.
Contents
A Quick Recap on the DLI
The daily light integral (DLI) is the total sum of PPFD over a 24 hour period. Ultimately, supplying an adequate amount of light is the single most important factor when it comes to plant lighting. If want to know more about DLI, we recommend reading our articles about the DLI in general or specific for the cannabis plant.
How To Calculate the DLI
There are two ways to calculate DLI:
Projected DLI (instant): Estimate the daily light integral by multiplying the current PPFD by the lamp’s photoperiod (the number of hours the light is on). This method is fast, simple, and ideal for grow lights with a consistent schedule, but it is not suitable for sunlight, where light intensity changes throughout the day.
← you can do this with every PAR meter
Actual DLI (24-hour measurement): Measure PPFD continuously over a full 24-hour period and integrate all measurements over time. This captures the actual amount of light your plants receive, including natural fluctuations from sunrise, sunset, clouds, and changing light intensity.
← this is what Apogee's DLI meters are for
Apogee DLI Meter Product Line
Apogee offers a product line of three different DLI meters covering different measurement aspects.
The user interface and software capabilities are the same on all three meters. The main difference is the accuracy and spectral sensitivity of PPFD measurements, which is also represented in the prices ranging from $300 to $600 as of July 2026.
The DLI-400 has the lowest-cost PAR sensor that is not representing the 400 to 700 nm PAR spectrum accurately for all light sources. It is therefore only recommended to measure natural sunlight.
The DLI-500 offers the same accuracy and spectral response as Apogee’s full-spectrum quantum sensors and can be used for any type of grow light – be it the sun, HPS, LED, MH, CMH, or anything else.
The DLI-600 is extending the 400 to 700 nm PAR spectrum into the infrared spectrum to provide an extended ePAR PPFD measurement. It can be used for any type of grow light as well.
Do You Really Need a Dedicated DLI Meter?
Before spending $600 on a device that does one job, it's worth asking whether your smartphone can already do it. With Photone, you get both DLI methods in one app. If you grow under artificial light only, you simply enter your photoperiod and the app calculates the projected DLI on the spot – no waiting, no logging, no extra hardware. And if sunlight is part of your setup, Photone can log PPFD over a full 24-hour period and give you the actual DLI, including every cloud, sunrise, and sunset along the way.
That covers the same two use cases as Apogee's product line, on a device you already own. A dedicated meter still has its place – if you need a sensor you can leave outdoors in the rain for weeks at a time, or if your workflow demands standalone logging across many locations at once, the DLI-500 or DLI-600 makes sense. For most growers, though, the app is the faster and far cheaper way to get the same number.
Thank you for reading and happy growing!
Sources
- The title image is taken from Apogee Instruments, Inc.'s website.
