Mars Hydro FC-E6500 Review

The New Mars-Hydro FC-E6500 is another game changer! The FC-E series are the first bar array fixtures that I have seen with adjustable bar positions. This cool feature allows growers to customize the distribution of light. There is a lot to like about the new FC-E series from Mars-Hydro!

The FC-E series have an elegant design that saves on shipping and is easy to assemble. I ran the FC-E6500 through four different PAR tests and it is among the most efficient fixtures that I have tested. At only about $750, the Mars-Hydro FC-E6500 has a cost efficiency of only $0.48/ µmol. The FC-E6500 has one of the very best prices for any light on the market. It is an incredibly good price for an innovative high-efficiency fixture. For the best prices, shop Mars-Hydro.com and use code: CCFC.

The Mars-Hydro FC-E6500 is in the same product class as the FC-6500 that I tested a couple months ago. They are both large bar array style fixtures meant for 5’ x 5’ coverage. The FC-6500 is a foldable fixture with 8 pre-mounted bars. The FC-E6500 comes disassembled rather than folded in half. There are only 6 bars on the FC-E6500, but they host more diodes and can be repositioned. The FC-6500 performed very well in my PAR tests, but the FC-E6500 performed even better. The FC-E6500 is a clear upgrade to the FC-6500 and it is significantly less expensive.

Being able to adjust the bars allows growers to move light away from the hot spot in the center and toward the edges. Along each bar Mars-Hydro also moves diodes away from the center and toward the ends. At each end of the bars the diode concentration is very dense, toward the middle of each bar there are relatively fewer diodes. This diode distribution along each bar coupled with the ability to slide bars closer to the edges, allows the Mars- Hydro FC-E6500 to produce a very even spread of light across a 5’ x 5’ canopy.

There are a lot of diodes. The FC-E6500 has a total of 3978 diodes which is over 6 diodes per watt! They are customized diodes designed for Mars-Hydro. They include diodes with different spectra. The full spectrum diodes are a mix of 3000k and 5000k. They also include red diodes at 660nm. The driver is a Moso X6-600M060A12. I do not have previous experience with Moso drivers. However, it performed very well during my tests. The maximum temperatures I measured were 57.1C (134.8F) on the driver and 59C (138.2) on the LED bars.

I really like the elegance of the design and how the fixture comes together. It consists of two sleek, light-weight aluminum frame pieces and the six LED bars. It is possible to mount the driver on the LED bars. They even provide a driver mount with adjustable width to accommodate the fact that you may reposition the bars. However, they also provide plenty of cable, which allows you to locate the driver elsewhere. Assembly is required, but it is pretty simple. Watch the video review to see the complete assembly process.

The adjustable bar position is a huge selling point for the FC-E series. I am thrilled to see this innovation. I often think about repositioning the bars when I am testing a fixture. This is the first fixture where that is actually possible. The bars slide freely along the frame and can be secured in almost any arrangement. Mars-Hydro suggests bar positions for two different set-ups with arrows on the frames indicating placement positions. Position 1 (see below) is a more standard arrangement of bars. However, the gaps between the bars are not even. There are larger gaps between the bars in the middle than on the top and bottom. Position 2 is a more radical arrangement. Two bars are close together on the top and bottom and the other two bars are spaced out in the middle.

I tested the Mars-Hydro FC-E6500 using both Position 1 and Position 2 shown above. Following our protocol, I tested each position with the maximum PPFD at 1000 µmol/m² for our official tests. I also tested each position at a higher hanging height. The FC-E6500 performed exceptionally well in all the tests. It is fascinating to consider how changing the bar position and the hanging height affected the distribution of density and the amount of light that reached the canopy.

In Position 1 (see image above), the FC-E6500 delivered a maximum PPFD of 1000 µmol/m² at a height of 30cm (12in). The average PPFD was 692.1 µmol/m², which is close to ideal. I measured a power draw of 642 watts and a Usable PPF of 1557.2 µmol, which means the FC-E6500 had a Usable Photon Efficiency of 2.43 µmol/w. This ties for the highest Usable Photon Efficiency that I have measured in a production model fixture. However, the distribution of light is not ideal at this height and bar arrangement. Much of the light is concentrated in the middle. Densities are great from top to bottom, but along the edges they are below the target of 500 µmol/m².

In Position 2, two of the bars are moved closer to the top and bottom. This improves the PPFD along the top and bottom of the map. However, the densities along the top and bottom of the map were already great in Position 1. Moving those bars helps to improve the densities in the corners, but otherwise the PPFD values along the sides are slightly worse.

In Position 2, I had to raise the Mars-Hydro FC-E6500 2 cm higher to a height of 32 cm (12.5in) to bring the maximum PPFD down to 1000 µmol/m². The hot spot was well off center below the two bars at the “bottom” of the map, which are close together in Position 2. I measured an average PPFD of 687.4 µmol/m², a Usable PPF of 1546.5 µmol and a Usable Photon Efficiency of 2.41 µmol/w. These are slightly lower than I measured in Position 1, which is predictable.

The amount of light that reaches the canopy is slightly reduced in the official test in Position 2 for two reasons: the fixture is 2cm higher and the sources of light were moved closer to the walls. When the bars are closer to the walls, more of the photons they generate will hit the walls and reflect. This is one of the tradeoffs between distribution and efficiency: It is most efficient to put the source of light right in the center, as far from the walls as possible. However, to get an even distribution, it is better to move the sources of light out towards the edge. Every fixture has to strike a balance between these competing goals. The Mars-Hydro FC-E series allows you some flexibility to strike your own balance.

In the official tests, with a maximum PPFD of 1000 µmol/m², The FC-E6500 has PPFD values below the target threshold on both sides of the map. The efforts to move diodes toward the ends of each bar contribute to a more even distribution than we would otherwise expect. However, at such a low hanging height, they cannot overcome the fact that the fixture is not as wide as the coverage area. In order to generate a better spread of light across the entire canopy the fixture must be raised slightly higher.

I ran Raised PAR tests at a height of 42 cm (16.5 in) in both Position 1 and Position 2. These maps produced much better distribution into the sides, at the expense of lower densities in the middle and a lower Usable PPF. At 42 cm, Position 2 has the highest corner values, but Position 1 has the best map overall.

The four tests that I did reveal some interesting patterns and we can learn a lot about the physics of light by studying them. With infinitely adjustable bar positions, there may very well be an alternative arrangement and hanging height that would produce an even better PAR map. I am curious what bar positions and hanging height you think would be the best.

We created a form where you could enter your suggestions to win the FC-E6500 that I tested. I selected 5 of the suggested set-ups and ran those tests in the summer of 2021. The grower who suggested the set-up that generated the best PAR map won the Mars-Hydro FC-E6500 that I tested. Check out my follow-up report and video documenting these tests and announcing the contest winner!

The new Mars-Hydro FC-E6500 is an exciting fixture. I have been waiting for a company to make an adjustable bar fixture and Mars has made a great one. It is easy to set-up and to reposition the bars. Both recommended positions have merits, and I love the ability to set any position that you want.

In terms of raw performance, the FC-E6500 is the best fixture that Mars-Hydro has produced. It has an industry leading efficiency along with the ability to customize the distribution. On top of that, the FC-E6500 has one of the absolute best prices on the market. It is less than 50 cents per micromole!!! The new FC-E6500 is clearly an excellent option if you are looking to light a 5’ x 5’ grow space. The smaller FC-E3000 (for 3’ x 3’ coverage) and FC-E4800 (for 4’ x 4’ coverage) will be excellent options for smaller spaces. For the best prices remember to use discount code CCFC on the Mars-Hydro website.