Using PAR meters to dial in and adjust the output of our reef tank LEDs has become the standard to really verify that we are providing the optimal environment for our corals. We have widely agreed upon PAR ranges specific to the type of corals we keep in our tanks, so it is just a matter of supplying our coral with those specific PAR ranges to optimize our success rates. 

Is it possible to set up and tune a reef tank LED light without using a PAR meter?

In this BRStv Investigates episode, we put the human eye and real-world experience to the test to find out just how well our eyes can measure or interpret changes in PAR. We asked six of our most experienced reef tank hobbyists, using only their knowledge and experience, to blindly guess the PAR ranges in an aquarium and then set up and tune a Radion G5 LED Light without a PAR meter. Ryan dives into the anatomy and science behind the human eye in an attempt to interpret our test results and further understand what we can do as hobbyists to maximize our success. 

Can They Guess The PAR?

In this first test, we asked our six experienced hobbyists to guess the PAR level in our Red Sea XXL750 office tank.  The tank is lit using four Radion XR30 G5 PRO fixtures with diffusers. The hobbyists were isolated in a different room as we adjusted the lights and then each of them was asked to come to observe the tank and guess the PAR. No reference point, just a blind test in which they were asked to leave in between changes to the light settings.  

Each hobbyist was presented with the same three color spectrums (10K, 20K, AB+) at both a 25% and 100% intensity at different times. These results would not only indicate whether or not the hobbyists could accurately gauge the PAR but also suggest how much spectrum affects that ability to register brightness and PAR. 

BRStv Investigates PAR Guess Results

The results were overwhelming in that our hobbyists only guessed 10 of 36 total measurement points within an acceptable range. Even the best of the lot, a guy who measures PAR for a living, performing with only a 66% success rate. So why did they perform so poorly? The answer lies within the anatomy of the human eye.

The Human Eye

The reason our team of reef nerds failed miserably was, for the most part, no fault of their own. Really no amount of experience will ever be enough to accurately measure PAR at a glance because of the way our eyes are built and function. Our eyes automatically adjust to whatever brightness conditions we are presented with making it all look the same. This makes it incredibly difficult, if not impossible, to see or gauge PAR, especially without any kind of reference point in which we can watch those levels change either higher or lower from a known PAR range.

Furthermore, the spectrum or color of the light plays tricks on us. Our eyes are much more sensitive to red and green colored light compared to blue colored light making it difficult to track changes in this cool color spectrum. This is exactly why a blue-colored 20K tank using 100% intensity looks dimmer than a 10K-14K tank at the same intensity, but will often measure with higher PAR when using a reef tank LED light. Our eyes and brain interpret blue-colored light as being relatively dim, regardless of the PAR level.  

Can They Find The LPS or SPS Sweet Spot?

Our second test was designed to see how well the team could do with the controls in their hands. We used the exact same Red Sea XXL750 tank lit with a bank of four Radion G5 Pros with diffusers installed. Each hobbyist was tasked with creating a 10k, 20K, and AB+ spectrum tuned for either LPS or SPS PAR ranges using the EcoTech Marine app.

We suspected this task to be easier. These Radion G5 LED lights are optimized to provide the right environment for SPS at 100% output over this particular aquarium, we tested the PAR levels ourselves. This group of hobbyists knows that which means each of them will have a general reference point when using the LED control sliders. For example, if 100% output is correct for SPS providing 300 PAR throughout, all sliders positioned at 50% should get us close to 150 PAR throughout. 

BRStv Investigates PAR Setting Results

The outcome was a similarly poor performance overall with only 14 accomplishments among the 36 PAR setting tasks we requested from the 6 highly experienced hobbyists. Breaking it down, we can determine that experience does help us to get close to the ideal spectrum and PAR range, especially when using the AB+ color spectrum. We just know what to expect in terms of output from the Radions when using this very common color spectrum.

That said, almost only matters in horseshoes and hand-grenades... getting "close" is not sufficient when we need exact PAR numbers for our corals to thrive. On top of that, finding that perfect PAR using a variety of color spectrums (10k, 20k, and AB+) further complicates the task at hand. The results clearly indicated that adjusting output correctly under 20K and 10K light spectrums was more difficult, presumably because of our eyes varying sensitivity to specific color spectrums. While it is possible to get it right with enough experience, developing confidence enough to adjust the LED light output each and every time in every color scenario is just not in the cards. 

At the end of the day, using a PAR meter to measure your light's output is, and always has been, the best choice for tuning your LED lights accurately. Thankfully, it is now easier than ever to get a hold of a PAR meter to set up and tune your reef tank lights with minimal investment.