AH-20 DLI Meter Sunlight Calculator Record MOL/(㎡d) for 10 Days,Full Sun,Partial Sun,Partial Shade,Shade

A reviewer said these did not work for their indoor plant lights but it worked perfectly for mine. I start seeds indoors and have used both flourescents and LED lights. The question is always how close to get the lights to the plants and how long to leave them on, without overdoing it and burning leaf tips. I bought three (for outdoor use) and was happy that all three read almost the same thing indoors on the 1st day -- close enough for what I need to know. The 2nd day, I put aluminum foil around the setup and all 3 readings jumped by 50%, the kind of thing I need to know.. My other need is to measure the relative levels of light at different spots in my yard, which gets filtered sun (and barely enough) so it's hard to know which is sunniest. I bought 3 so I could compare three different spots on the same day. It has already told me that a spot I thought was a little sunnier actually gets about 10% less over the course of the day, and it was reassuring that I got the same result when I reversed the placement of the three devices the next day. I'll be repeating this around the yard, comparing different spots. I wish I could give only 4.5 stars because the instructions are bad and they have limited applications. I had to read other reviewers' comments, which were very good -- THANK YOU!!! -- to know how they work, and what the number means. (It gives you one number, telling you the total amount of light that the spot gets each day, nothing else. It saves nine numbers.) I also had to look at other reviewer's comments (and Google) to get a better feel for how much light is enough for different plants. It's a little weird that the device is so absurdly simple that you can't turn these devices off except by taking out the battery, and you must remove four little screws to replace that AAA battery. They all arrived with a dead battery in place but came with a second battery and a nice little screwdriver so it was fine, but odd. The tiny clear (silicone?) washers that presumably waterproof the screw hole are too flexible so maybe the device won't last in a high humidity environment; I don't know. I was tempted to give them only 4 stars but for 20$, they told me exactly what I needed to know, both indoors and outdoors, and one might have been enough, so that's hard to beat.

This meter has no warranty other than the 30-day Amazon return policy. Mine lasted about four months of outside use in Hawaii. Tried a new battery, just in case, but it made no difference.

It's well made with bright large numerals. The trick is understanding how to use it. This is what I do: I set it in the outside location the night before. At midnight, the data in memory location zero is moved to location 1 and location zero is scrubbed. Data starts to accumulate in location zero and you may view it at any time by pressing the button. Once again, at midnight, the total amount of photons in location zero gets moved to location 1, 1 gets moved to 2, and so on. Location zero is now ready to get new data again. It's very ingenious and works well. I do recommend it.

Couldn’t figure out how to use it

This worked well while it lasted (which was less than a year). I left it outside for most of the winter (which in coastal Oregon means much rain but no snow or freezing temperatures). Upon trying to use it this spring, I found that the battery was drained, which was not unexpected. However, when I opened up the light meter to replace the battery, there was a substantial amount of water inside it, despite a rubber gasket sealing it. I dried it out in a desiccant bag for two days, but the display is partially not working now, and I can't tell what the readings say. I'll have to throw it away.

I started by using this sunlight calculator to measure my indoor grow lights. It didn’t work. I tried under two different lights over the course of a week. The numbers were in the decimals and lower than an hour, not making sense at all.So I took it outside to the brightest spot on my patio. I got 9 hours of actual sunlight (give or take), which made more sense. I left it there for a few days, then moved it to a shadier spot. 5-6 hours of sunlight since it had also been cloudier. So it does work outside, but not under grow lights. Also, this sunlight meter is low tech and I couldn’t figure out how to reset it back to Day 1. If you plan on moving it more often than every 10 days you will need to keep track somehow of what day you are on (mentally or on paper).There has been a learning curve, but over time I have discovered that the sun/shade moves about an inch per hour of sunlight on my patio. The total amount of light changes, of course, as the days get longer/shorter depending on what side of the calendar we are on. For this spring/summer I have been better able to arrange my plants to prevent sunburn of some and allow others to thrive more. I have also been able to better determine how much sun the plants on the lower shelves are actually getting (picture shows that on Day 6 the shelf got 1.4 hours of sun total). During fall I will use to place items into my greenhouse based on their light needs and how much light each section actually gets..I like that the stick part of the device is long enough to keep it upright in soil. It is also a sturdy plastic so no rust to worry about.Update: I figured out this device and found it helpful….but it stopped working after just a few months. It did not get wet at any point since it’s on a patio. I did not drop it. It just won’t turn on now. And there is no way to replace the battery. Disappointing.

It gives u an idea how much sun light a given spot is getting. It keeps history for past days. I just wish I know how to turn it off when I don't need it anymore. Just seems to continue to measure light even when I put it away.

Only worked a few weeks. Past return window otherwise would have returned.