ViparSpectra XS1500 Pro Review

The XS1500 Pro is the newest light from ViparSpectra! They are bucking the trend we have seen in the last several years and are doing something that most other manufacturers have given up on… They are using lenses to achieve the best distribution of light across the canopy. And it works!

The ViparSpectra XS1500 Pro is the first light in the new XS Pro Series. It is similar to the XS series but has some notable differences. They are both quantum board style fixtures with ribbed aluminum heat sinks, attached drivers, and integrated dimmers. The new XS Pro series features the Samsung LM 281B diodes. The XS1500 Pro has a total of 450 diodes, which is exactly 3 diodes per watt or 0.33 watts per diode. They use 3000k and 5000k full spectrum white diodes along with 660nm deep red and 730nm far-red diodes. On top of the heat sink, the XS1500 Pro has a Sosen SS-150VA-56B driver. Growers may complain that these are not the Samsung LM 301b diodes with a Meanwell driver. However, the measured performance of the new XS1500 Pro model is significantly better than the original XS series fixtures.

Quantum board style fixtures were revolutionary several years ago. They brought manufacturing costs down and allowed excellent efficiency for the cost. However, their relatively small form factor leads to some drawbacks. To get good distribution, most quantum board style lights require a significant distance between the fixture and the canopy. Even with enough height, the density of light on the edges and in the corners is usually suboptimal. LED bar fixtures resolve this issue by spreading the source of light over a larger area. The result is a more uniform distribution of light which allows a lower hanging height. In most larger spaces you will now find LED bar fixtures rather than quantum board style fixtures. However, quantum boards remain the preferred choice in smaller spaces.

Some early quantum board fixtures used lenses to even out the distribution of light. However, lenses lead to slightly lower efficacy because some of the light becomes heat as it passes through the lens. For much of the last decade, the grow light market has been hyper focused on efficacy. Manufacturers wanted good numbers to convince growers to upgrade from HPS and other gas discharge lights. Furthermore, high efficiency fixtures could qualify for rebates in some markets. With the focus on efficacy rather than distribution, most manufacturers abandoned lenses.

PAR testing has brought more attention to distribution. For smaller fixtures that are often run in single fixture grows, the ability to fully cover the area is paramount. ViparSpectra is leading the industry now with multiple novel and successful ways to improve the uniformity of distribution. It is clearly one of their top goals. When I reported the results of my tests with the XS1500 Pro, their first question to me was, “does it earn an A+ grade from you for distribution”. Indeed, it does!

I ran several tests with the new ViparSpectra XS1500 Pro. To begin, I set it up in a 2’ x 2’ area and ran the official PAR and ePAR tests. I run my official tests at the hanging height that delivers a maximum PPFD of 1000 µmol/m². For the XS1500 Pro, that was 32 cm (12.5in) above the sensor.

The PAR and ePAR maps from these tests are excellent. The values are all high and in a very tight range, the distribution of light is impressive and unique. The highest and lowest values are along the edge, not in the middle or in the corners. All of the values are excellent, but moving across the map, the values seem to go up and down randomly. Furthermore, as I was running the tests, I saw that the sensor was more sensitive than normal. Small changes in sensor position could lead to notable differences in density.

I decided to run tests with an increased sampling density to better understand the distribution of light. In most PAR tests, we take one density measurement per 15cm (6”) square. As you may have seen in my videos, I take the sample from the center of each test grid square. That value is meant to be representative of the entire square from which it was taken. However, if I want to learn more fine-grained details about the distribution of light then I can increase the sampling density within each square. I ran PAR and ePAR tests with 9 sample measurements in each test grid square.

The results are certainly interesting, but first and foremost, they are impressive. The densities are high everywhere, even right up to the edges and deep into the corners. The base of the sensor was touching both walls in the corners and the densities are all still excellent. For the purpose of using this light to grow plants – that is the most important factor. However, for the purpose of understanding the physics, I want to dive deeper!

The high sample density test with 9 samples per test grid square is on the left with the complete data for the test. In the middle map, I show just the center values from each test grid square. In the far right, I show the average from the 9 measurements in each test grid square. Below those maps I show the difference between the center value and the average value.

When I was first establishing our current Grow Light Testing Protocol, I ran several tests and analyses like this with different fixtures. I wanted to ensure that one measurement every 15cm (6”) was adequate to get a reliable average PPFD. In those tests, I was actually surprised how similar the results were from the center and the average. Square by square the values would differ a little, but the overall averages were always nearly identical. That convinced me that the sampling frame was adequate and would generate accurate Average PPFD measurements.

That turns out not to be the case with the XS1500 Pro. You can see above that at 32cm, the center values in most squares are significantly higher than the average values of the 9 measurements from the square. This is particularly true for the corners. Therefore, we cannot rely on the center values to determine the overall average (e)PPFD, usable (e)PPF, and Photon Efficacies in these tests.

So, what explains this? ViparSpectra uses lenses to aim the light at specific areas that are normally underlit. The corners in particular seem to be boosted by the lenses. It makes sense that the light is focused on the center of those squares. Although the center of the squares are above average for the square, there are no bad areas in the whole map. The distribution really is impressive, and I am certainly splitting a few hairs!

For our purposes it is simply worth noting that for this fixture at this height, measuring only the center of each square will lead to a sampling error. The center values skew higher than the true average for the individual test grid squares. Therefore, I use the statistics from the full high sample density test as our official measurements for the ViparSpectra XS1500 Pro.

The 32cm tests got me thinking. If they really are aiming the light at specific areas on the edge of the canopy, then what happens if we change the hanging height? I decided to find out.

I raised the XS1500 Pro to 41cm (16in) above the sensors. This is typically a good height to set a light in your grow if the minimum hanging height is about 12 inches. I ran a high sampling density ePAR test.

Again, really impressive and very interesting results. Excellent density numbers everywhere. And a very uniform distribution overall. But it is different. The lowest PPFD is 715 µmol/m², but you’ll have to look for it because it is not in a corner or even along the edge. The most surprising twist is the highest PPFD I found in this test is in the bottom left corner! I have never seen that before. I suspect that the light which was aimed at the middle of the square at 32cm is now hitting further into the corner at 41cm.

At 41cm, the Average PPFD is lower than in the 32cm test. This is true with all fixtures because more light reflects off the walls at a higher height. However, the ViparSpectra XS1500 Pro aims light out toward the edges so that effect may be more pronounced. But again, I am splitting hairs because it is interesting. Overall, the distribution here is uniform and excellent.

Interestingly, the center value and the average values from each test grid square agreed in this test. There were differences in several individual squares, but overall, those differences wash out. There is almost no difference in the overall averages. This is a typical result when I run a high sample density test. It was exceptional that at 32cm there was a significant difference.

I often run a test where the fixture is higher than the official test, like I did here. I do not usually run tests at a lower height because the densities will be too high for most grows. However, with the ViparSpectra XS1500 PRO, I wanted to see how a lower hanging height would impact the distribution and where the light was focused.

I lowered the ViparSpectra XS1500 Pro to 25.5cm (10in). This is only 2.5 inches lower than the official test and many growers may let their plants get this close. I ran a high sample density ePAR test.

The distribution of light in this test is still very impressive. The XS1500 Pro is a relatively small fixture, and it is hung only 10.5 inches above the sensor. Despite that, the PPFD is still great, even deep into the corners. However, we can see that it is less uniform than it was at higher heights.

The maximum PAR PPFD at this height was 1191 µmol/m², and the maximum ePAR ePPFD is 1240 µmol/m². These light levels will put significant stress on plants grown without supplemental carbon dioxide, so it will be best for most growers to avoid allowing the plants to get within 12 inches of the XS1500 Pro at full power. In a 2’ x 2’ tent, 13-16 inches is great – anything less is potentially dangerous.

Looking at the Center Values and the Average Values from each square in this test we can see that the sampling bias is back strong. Because of the way that the ViparSpectra engineers are strategically aiming the light at the canopy the center point measurement from each square is almost 45 points higher than the true averages in this test. This is not significant for growing with the fixture, but it must be accounted for to accurately measure the performance of this fixture. In this test, the ViparSpectra XS1500 Pro had an incredible Photon Efficacy of 2.30 µmol/w. However, if I had only tested the center of each square, I would have overestimated the photon efficacy to be 2.41 µmol/w.

Before testing the XS1500 Pro, I thought the PAR maps ViparSPectra had made were too good to be true. I was excited to test it and see if I could figure out the catch. However, all of the PAR and ePAR tests really impressed me. They are getting exceptionally even distribution from this little quantum board style light. And they are keeping excellent Photon Efficacies despite using lenses. I am certainly impressed.

After running the PAR and ePAR tests, I tested the on-board dimmer. Previous ViparSpectra models have used a continuously variable dimmer. In contrast, the new XS1500 Pro has a dimmer with preset positions at 5%, 25%, 50%, 75%, and 100%. As you can see in the chart, the dimmer is accurate throughout the dimming range.

I also measured the operating temperatures on the ViparSpectra XS1500 Pro. The aluminum ribbed heat sink reached a peak temperature of 57.3 C (135.1 F). The Sosen driver hit a maximum surface temperature of 60.0 C (140 F). Surface temperatures do not reflect how much heat will be added to the grow space. Instead, surface temperatures show how effectively the fixture distributes the heat. It is important because cooler fixtures run more efficiently. Like all lights, the amount of heat that they add depends on the power draw. With 153 watts of power in my tests, the XS1500 Pro will add about 520 BTU/hour to a grow space.

The ViparSpectra XS1500 Pro is fascinating on many levels. They are effectively using lenses to promote uniform distribution. The performance is excellent with remarkable distribution of light and great photon efficacy. To top it off, it is really a great deal! It is currently listed on Amazon for about $140 which would be a great price, but there are two big discounts. First, click the $40 off coupon on the Amazon Product Page! Then, during Checkout, enter discount code DrMJCocoPro for an additional 8% off. Your final price will be only about $92.00. That gives it a cost efficiency of only about $0.30/µmol. It is one of the best prices you will find on any light!

Although I do not expect many LED bar arrays will adopt lenses, ViparSpectra is showing us that they can be effective with small quantum boards. I think quantum boards still have a lot to offer growers in smaller spaces. The XS1500 Pro resolves the common quantum board issue of poor distribution. I would not be surprised to see more small quantum boards follow ViparSpectra and return to using lenses, but they’ll be tough to catch! The XS1500 is a great little light at an incredible price. If I needed to buy a 2×2 light, it would go in my cart!