First things first: LEDs?
LED stands for light emitting diode. So what’s a diode?
A diode, pictured below, is an electronic component with two points of opposite charge. In between those two points is a semiconductor. The semiconductor acts on the electric current as that current passes across the two points of the diode, dropping down the energy levels of the electrons in the current. It may help to think of the semiconductor as a permeable surface that allows the electrons to fall down out of their normal orbits, much like a sieve. The energy released in that reaction is what produces light, and in more wasteful systems, heat. The differences between semiconductors will produce various colors of light like the blue ones the scientists who won the Nobel Prize discovered.
What really matters more than the explanation is why that technology is better. The answer to that question lies in its efficacy.
Efficacy is measured by the number of lumens per watt a light source produces. To break it down a bit further, a lumen is a measurement of the amount of light a source produces while a watt is the amount of energy a source uses.
Efficacy proxies how efficient a light source is at converting energy to light. The higher the efficacy, the more efficient the bulb is, and the more efficient the bulb is, the less energy wasted as heat loss.
So let’s first look at traditional horticultural lighting. These are the long, fluorescent lights greenhouses use in winter months or people may use indoors to start seedlings.
Another common type of horticultural light are high-intensity discharge (HID) bulbs. I can talk more specifically about how they compare to LEDs at a later time, but for now I’ll just mention that I chose not to analyze HIDs in this piece because of a number of variables that make that analysis difficult over time. Those variables include uneven life-cycle watt usage, fading of the light, and disposal issues derived from certain chemicals integral to the HID’s function.
Here’s the top result on my google search for fluorescent lights and a bit of the sales copy from that page in bullet form:
- Four 2’ Compact T5 High Output Bulbs 6400K GROW BULBS Included (PLL-55W)
- Compact T5 bulbs have an outstanding 20,000 hour life expectancy (one year is 8,760 hours) and unlike sodium or halide bulbs, a T5 loses very little of its’ light output over its’ life.
- High Output bulbs have extremely high lumen per watt rating – 5,000 lumens per bulb! This system emits an incredible 20,000 lumens!
- Lamps emit very little heat, allowing you to hang the fixture very close the the plant canopy. THIS DRAMATICALLY INCREASES YOUR YIELDS!
Further reading shows the efficacy: 92-lumens/watt. To produce those 92-lumens/watt, this unit takes up 24”x24” feet of space at a total cost of 134.95.
Now we have a frame of reference for the fluorescent lights. I’ve never used this product, so can no way comment on its productive capabilities, but this information is useful for comparative purposes nonetheless.
Compared to the stagnant development of fluorescent lights, records are being set in the world of LED lighting as recently as March. Manufacturer CREE set the record for the most efficient bulb ever, producing over 300-lumens/watt. That’s three times the efficiency of the fluorescent lighting system. Unfortunately, these lights aren’t expected to hit the market for at least another year.
In terms of products out now, check out this ranking fromhttp://plantozoid.com/.
The top-ranked product is the Diamond Series XML 350 and it will cost you $549; more if you want to scale up production for commercial purposes. Regardless, these LED stats are so much better than the fluorescent bulb we looked at.
First of all, we are looking at a light that is going to last more than twice as long as the fluorescent model above. Unfortunately, instead of lumens, the Diamond Series lists coverage in sq. footage so we don’t have an exactly equal comparison here, but one rule of thumb says that you need around 2000 lumens per square foot for light intensive crops. So if we are covering 20+ square feet, we are looking at 40,000 lumens giving us a rate of 121-lumens/watt.
That’s certainly more efficient than fluorescent, but there are trade-offs in areas like initial cost. However, once that cost is overcome, and especially as the technology improves, it will be inconceivable not to use LEDs in vertical farms.
So let’s take a brief look at the pros and cons of LED lights as the technology currently stands:
- Can produce dual band color spectrum (red and blue) at the same time. Plus by tailoring the light to the specific part of the spectrum that plants use to make energy, LEDs ensure no light is left unused
- Highly energy-efficient—nearly all wattage is converted into usable light
- Minimal heat production reduces A/C and heat sink costs
- Expensive to purchase—LED rigs can cost as much as large HID assemblies yet deliver light to less square-footage (note, in my above comparison, I looked at two lighting units that were in the same size range of the actual hardware, not the size of the space they lit)
I want to highlight again cost is only a short term problem. As shown in the graph above, LEDs are only getting cheaper and the energy savings that they already provide let them pay for themselves in just a few years. This brings us to our next point- the implications of increasing growth efficiency through LEDs.