Over the eons, mankind has strived to both see the light and effectively use and improve it, both for necessity and for expanding time and awareness.
Let’s start with a little history. The very first light fixture is thought to have been manufactured around 70,000 B.C. It was composed of a sea shell reflector, moss filament and animal fat as an energy source. Fast-forward to around 3,000 B.C. when the Chinese mass-produced the first reflector. The Yan Suis (solar igniter) was a small mini-parabolic sun mirror used by all young men and worn on their belt.
Producing roughly 30,000 a day, these units were used for starting fires and, as some speculate, for sending signals and for the Confucius warriors to blind their enemies. Around 1,000 A.D., there were Roman street lights. In 1879, we got the first incandescent light bulb and in 1901 we saw the first mercury vapor, followed by the first florescent lamp in 1926. Finally, in 1996 we saw the first LED.
Hands-on Testing of LED Grow Lights
In late 1998, I worked with a company on one of the first LED fixtures for horticultural testing. At the time, I was handling the build-out and development of Bloomington Wholesale Garden Supply (BWGS). The manufacturer asked me what I would like him to make and send for testing. He wanted my suggestion on light output, footprint coverage and color. I suggested a fixture that would put out the same as a 400W MH or HPS lamp.
I’ve always enjoyed testing new technologies to see how they stack up with the existing products. This ended up being a very big light and it required very deep pockets. The unit failed on both performance and cost. The lumen-per-watt was quite low in comparison to today. As with items like computers, calculators and solar panels, prices have dropped incredibly with vastly increased production.
In 2004, I was asked to present to the Shenzhen LED Association in China. This was to discuss the future needs and applications for manufacturers. At the time, there were about 2,000 LED manufacturers in the city of Shenzhen alone. I brought in several physicists from large multi-national companies to present. In my opinion, the products at that time had not reached the needed efficiency/cost level for the marketplace.
Some Useful Definitions Regarding LEDs
Let’s pause for some definitions. The LED is extremely efficient and produces up to 98 per cent useable light. The color and spectrum can be anything you want, but they have to be defined. LED is a one-sided light source (or plane source). LEDs do not require a reflector, so non-reflector LED fixtures use a plane light source. This means much more usable light for plants, and if correctly designed, will produce more performance in plant production.
Because LED technology has higher efficiency, with heat evenly distributed via the plane source, an LED light can be placed much closer to plants. This lowers the required wattage. Since LED lights can be used closer to plants, the power to run LED lights can be greatly reduced compared to other lighting technologies and their higher wattage systems. Inverse-square law is a physics rule that helps to understand this. It is also affected in some cases, such as fluorescent, by the milliamp output.
In other words, the light drops drastically the further the fixture is placed from the plants. The LED also drastically reduces heat at the plant level because of even distribution. This is where the physicists, electronic engineers and horticultural testers come in—defining, refining and testing.
Another key factor in LED development for horticulture is lumens per watt (the amount of light output per watt). The majority of current LED lights operate at 110-120 lumens per watt, but some manufacturers are producing considerably more lumen per watt. One Korean design is producing 140 lumens per watt. However, that design uses a single point source and expands the light with a reflector, which drops the fixture’s efficiency significantly.
Different Lighting Technologies
The sodium light also operates at about 140 lumens per watt. The point source must be converted to plane source (usable light) via geometry and a reflector. Plant elevation is set by reflector design, point source and heat output. In other words, the light has to be both expanded from the arc tube and kept far enough to divert heat and get the light spread out enough from the reflector. The light also has to bounce off the reflector and down and out. Usable light drops off 10-20 per cent.
For wider coverage, it also has to be raised enough over the plants to get even distribution, and this is set by the reflector. Every foot raised in elevation over the plants is a drastic lumen reduction. Lumens fall off hard the farther you are from the light source. The light intensity on the plant is 1/d2 from the light, where ‘d’ is the distance between the light and the plant. For example, reducing the distance between light and plant from two feet to one foot means the plant will have four times the light.
Much of the heat is also focused to the arc tube rather than evenly distributed on a sodium fixture. Arc tubes run at roughly 900˚F and the lamp at 550˚F on a sodium lamp (on both 400W and 1,000W models). The heat can be reduced with fans, but the point source and reflector determine elevation via lumen distribution.
HO 54W T5 lights are defined by the type of phosphorous used and the milliamps (mA). They also utilize point source but distribute the heat better and end up with a much larger point source distribution. The lumen output per watt starts at roughly 90 lumens per watt. Usable light is improved via the reduced elevation over the plants. The T5 point source is distributed over the entire lamp. The light output of a fluorescent lamp is proportioned to the power of the lamp. When the lamp current is dropped from 450 mA to 350 mA, the lamp power is dropped, too. Therefore, the light output is dropped as well.
New LED Strip Light Fixture and T5 LED Replacement Lamps
Now that we’ve covered some of the basics, let’s move on to the latest LEDs. These LEDs were tested and met some new criteria. Their minimum was 130 lumens per watt. They are 6.5 Kelvin and 3K full spectrum (high CRI) LEDs. They promise a reasonable return on investment within two years and are convertible for existing hydroponic gear because they are similar to and a direct replacement for T5 fixtures. These new LEDs are actually strip lights, and this is what I tested.
The first test of the LED strip light was a direct control for propagation between four-lamp T5 HO 220W fixtures and four-lamp 136W LEDs. Both types of the HO T5, the 350mA and 450mA fixtures, (450mA put out 30 per cent more lumens than the 350mA), were tested against the LED 136W fixture. All fixtures were 6.5K. The T5 was tested only with Japanese tri-phosphorous lamps because Chinese phosphorous T5 lamps drop off in lumens too quickly. Some growers have to replace them every three months, whereas tri-phosphorous lamps can go up to18 months.
The LED 136W outperformed both T5s in plant production in controls and in the greenhouse. Energy and heat were both reduced by 33 per cent over the T5. The unit cost on the LED was higher than the T5 but also pays for itself within two years through energy savings. This is without factoring in the extended lamp life of the LED. Both T5 and LED plants could be transferred to direct sunlight but with shock.
T5 LED Replacement Lamp Tests
I also tested the new T5 LED direct replacement lamps. These were direct replacements and did not require rewiring or a ballast change to the driver in the T5 fixture. You just plug the LED lamp directly into the T5 fixture. The first test was 3,000-lumen LED lamps in comparison to standard T5 fluorescent lamps. The LEDs outperformed all typical T5 lamps excluding the 450 mA tri-phosphorous lamps. Those 450mA Japanese tri-phosphorous T5s outperformed the 3,000-lumen LED.
Next, the 4,000-lumen replacement LED lamps were tested against the T5 fixtures with the 350mA and 450mA tri-phosphorous lamps. The 4,000-lumen LED lamp outperformed all the T5 H 54W fixtures and lamps.
High Output 230W T5 LED Strip Light Fixture
The last test was with a 230W LED strip light fixture and a 400W sodium fixture. Bell pepper and tomato seedlings were all started with HO 54W 6.5K T5 fixtures. The plants were then control-tested with LED 6.5K, LED 3K, and sodium 400W. The LED 6.5K outperformed with bell pepper production. The LED 3K outperformed with tomato production. The sodium was set at the lowest possible level with controlled ventilation.
The LED fixtures ran at 100˚F. The sodium lamp ran at a focused 550˚F. The LED fixtures had 50 per cent greater plant coverage than the sodium lamp. The LEDs did not need protective barriers to keep the light contained to the grow area, whereas the sodium lamp did. The LED plants transplanted easily to direct sunlight, but the sodium plants required hardening.
Lighting has come a long way in the last 72,000 years. There have been fantastic advances in LEDs over the last 20 years. The very latest LEDs are now proving themselves more than competitive with previous technologies due to improved lumen per watt output, plane source lighting, heat reduction, energy reduction, and longer lamp life. Also, many thanks to Hydrofarm, Grodan and the many other manufacturers over the years for their contributions with the continued testing.