How Many SolStrips for My Space?

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Dual SolStix Rax vegging

The most common question gardeners have when considering a SolStrip system is, how much light do they need for their space? Because LEDs are so much more efficient than high-intensity discharge (HID) and florescent lights, the traditional rules of thumb for light intensity, expressed in watts per square foot, aren’t applicable to SolStrip systems.

Current state-of-the-art white LEDs are up to 50% more efficient than HID lamps such as metal halide and high-pressure sodium lights. That huge boost in efficiency not only means more light per watt consumed, but also less heat given off by the lamp. SolStrips leverage that efficiency further with distributed diode technology, which spreads the light emitters, and the heat, across a much larger area than HID lamps or even COB lights.

Together that means that SolStrip lamp systems deliver more light per watt and can be placed much closer to the canopy, where they will deliver that light much more evenly and coolly than HID lamps. All  of these factors must be considered when estimating light needs using SolStrips.

Rule of Thumb: 35 w/sf

The rule of thumb you should use when planning a SolStrip system is 20-30 watts of light per square foot for vegetative spaces, and 30-40 w/sf for bloom spaces. For a mixed veg/bloom space use 35 w/sf. These are fairly broad ranges admittedly, but be wary of operating outside of them. Below 20 w/sf will result in stretching and thinning of vegetation; above 40 w/sf can lead to bleaching and die-off of tops.

This rule of thumb presumes several conditions:

  • The watt total is operating watts, not potential watts. SolStrip X2’s have the potential to deliver 48 watts of light per strip, but most gardeners will operate them softer in the 33-42 watt range. Use the operating wattage for your calculations.
  • The light system will be positioned 12” above the canopy. The physics of light means that its strength decreases exponentially with increasing distance. Positioning your lights 18” above the canopy will only give you 50% of the intensity of the same lights at 12”, at 24” your lights with deliver only 25% of the intensity at 12”. Conversely, positioning your light 6” above the canopy (very possible due to SolStrips’ very low heat) will double your light intensity from 12”.
  • The light system will be designed to distribute the SolStrips evenly across the growing space. SolStrip LEDs emit light in vertical cone of about 120 degrees. No light is wasted as in HIDs by being sprayed in a 360 degree pattern that must be reflected back onto the canopy, with all the waste and weakening of intensity that results. But that means SolStrips must be aimed directly at the canopy from directly above.

Practically speaking, that means you can estimate coverage for SolStrip systems using 30 w/sf and running your system at 100% of potential output:

  • SolSheet Original: 5 sf, with a 36” x 20” footprint
  • SolSheet X: 8 sf, with a 42” x 28” footprint
  • SolSheet DBLX: 16 sf, 48″ x 48″ footprint at 18″ vertical height
  • SolStix Rax DBLX array of twelve X2 or eight X3 strips: 25 sf, with a 60” x 60” footprint at 18″ vertical height

These are guidelines only. If you plan to run your lights softer, or higher than 12”, you’ll need to account for that in your estimate. For those willing to do a little math, there are better measures of photonic energy, i.e., light, that will deliver more accurate calculations based on values such as PAR and PFFD. We will explore those in a future post. But for basic planning in a typical indoor gardening space you can use these calculations with confidence.

Driver Selection

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Once you’ve chosen your LED lamp design, calculated your coverage needs, and chosen your color spectrum, the next step is to decide which power supply or driver you need to power your light.

The truth is there are many possible options for your choice of driver depending on the number of strips per circuit, and the type and design of your circuits. But the mission of Photon Solutions is to bring simplicity to LED DIY, so based on a parallel-wired system, these are my basic driver suggestions:

  • 3 SolStrip X2s: CLG-100-24A or HLG-150H-24A
  • 2 SolStrip X3s: HLG-150H-24A
  • 4 SolStrip X2s: HLG-185H-24A 
  • 3 SolStrip X3s: HLG-240H-24A
  • 5 SolStrip X2s: HLG-185H-24A or HLG-240H-24A 
  • 4 SolStrip X3s: HLG-240H-24A or HLG-320H-24A
  • 6-8 SolStrip X2s: HLG-240H-24A or HLG-320H-24A 
  • 5 SolStrip X3s: HLG-320H-24A
  • 8-12 SolStrip X2s: HLG-320H-24A or HLG-480H-24A
  • 6 SolStrip X3s: HLG-480H-24A

I highly recommend getting the lower powered driver over the higher power suggestion. The physics of LED chips make them most efficient at about 70% of their rated max, or about 33-36 watts for SolStrip X2s. You can drive them at 100% if you want, presuming you keep them cooled within their operating range (I aim for 50-60C max). But you will get less than 15% more light for expending 30% more electricity. For example, while the 100w CLG will max out at a very efficient 33w/strip on at SolSheet Original, the 150w HLG will max out the strip’s 50w capacity and then some, as the HLGs tend to run about 15% above their rated power (~165w). That means you’ll end up dimming the driver down to just to operate the strips at 100% of their rated power. You will be running both the strips and the driver below their peak efficiency.

LED DIY Rule #1: Run your LEDs soft; and your drivers hard

Running your strips at around 70% by using a driver which has a maximum output slightly below the total maximum rating of the SolStrip circuit (using 50w X number of strips) makes for the most efficient and cost-effective use of both the SolStrips and the driver. The LEDs are most efficient at around 2/3 of their max output, and the drivers are most efficient when run at 100% of their max output. LEDs aren’t like HID bulbs, which are optimized to run only at their maximum rated power. LEDs are more like cars, able to operate across a range of output, with a maximum and minimum wattage, and an efficiency sweet spot somewhere in-between. Aim for the sweet-spot when selecting your driver, not the maximum. You’ll save money and be more satisfied with your results.