BloomStar ePAR Meter Review: How to find the dimming level & lamp distance that truly fit the phase

I like dimmable LEDs. Really. But I also noticed: Dimming without measurement is often just guesswork. Sometimes everything looks "okay," but growth is sluggish. Sometimes you think you're going full throttle, and suddenly the leaves look stressed, become wavy, or show visible burns. This is exactly where the BloomStar ePAR Meter picked me up: I no longer wanted to set things by feel, but in a way that I have a solid light base for each phase and thus not leave growth and yield to chance.

It turns "turn on the lamp and hope" into a repeatable routine: Check distance → measure PPFD → dim → keep an eye on DLI → done.

What exactly does the device measure – and why is it so practical with LEDs?

For me, the ePAR Meter is not a toy, but an adjustment tool. It turns "turn on the lamp and hope" into a routine I can repeat: Measure, adjust, measure again – done. And the best part: I can use it to sensibly determine both the dimming level and the lamp distance. These two adjustment screws ultimately decide whether a plant grows relaxed or is constantly at its limit.

What exactly does the device measure – and why is it so helpful with LEDs?

The BloomStar ePAR Meter measures ePAR in the range of 400 to 750 nm. This means it's not about how bright the light appears to our eyes, but about the range that plants actually use for photosynthesis. I used to often work with "looks bright enough" – but that's simply unreliable with LEDs, because different spectra can appear differently to us, even though the plant ultimately receives more or less usable light.

With the ePAR Meter, I instead look at PPFD, i.e., the instantaneous value of photons reaching the canopy. And that's the core for me: PPFD tells me directly whether I'm currently in a range that suits the phase – or whether I'm giving too much or too little.

My setup workflow: How I set dimming level and distance

I keep it deliberately simple, because otherwise nobody will stick with it long-term. My routine looks like this:

First: I always measure at plant height, directly at the canopy. This is the point where the plant actually receives the light. If you measure somewhere in between or too high, you get values that in practice do not reflect what is happening at the top of the leaves.

Second: I don't just measure in the middle. The middle is almost always the most brightly lit, so everything quickly looks great – until you realize that the edges are lagging. That's why I do a small mini-mapping: middle, then several points towards the edge and corners. I don't care if every point is perfectly identical. I just want to avoid having extreme outliers. If the edges are much too low, there's no point in only optimizing the middle.

Third: I work in two steps. First, I set the distance roughly so that the illumination is reasonably even. Then I use dimming for fine-tuning. This has proven to be the fastest way for me. Distance tends to influence distribution, dimming tends to influence the total amount; if you separate these, you get a "rounder" result faster.

Fourth: I use DLI as a plausibility check, especially during phase changes or when I'm adjusting the lighting duration. PPFD is the instantaneous value. DLI is what accumulates over the day. Especially when reducing or increasing hours, you can better assess whether you should readjust via dimming or distance.

What I actually use in everyday life

In practice, however, it's primarily the hold function that I constantly use: measure value, hold briefly, read, move on to the next point. This saves nerves, because you're not always ideally positioned when measuring at the canopy.

Common mistakes you can avoid

The most important thing is really the position of the probe. If you don't measure at canopy height or hold the sensor at an angle, you quickly get nonsense. And if the device doesn't show anything sensible, in practice it's usually because the sensor or cable isn't properly seated or the batteries are dead. Sounds trivial, but these little things otherwise cost time when you "just wanted to measure quickly."

Who benefits from the BloomStar ePAR Meter?

If you have a dimmable LED or regularly adjust the distance, in my opinion it's very worthwhile. Because it allows you to precisely hit the two most important adjustment screws: How much light am I actually providing at the canopy – and how evenly is it distributed across the area?

I find it particularly useful if you want to intentionally manage phases: young plants and cuttings need something different than the growth phase, and the flowering or fruiting phase is another matter entirely. With the ePAR Meter, I can do all of this much more controllably, instead of just relying on "looks good."

My Conclusion

The BloomStar ePAR Meter brings calm to my setup. I no longer adjust the lamp by feel, but by measured values. This allows me to find the right dimming level and lamp distance for each phase more quickly. And that's ultimately the lever: stable development, fewer stress signs, more even area – and thus, in total, usually also better results.