In April of 2021, Comm Bank Stadium announced the arrival of the first set of LED turf grow lights in Australia. Using LED grass grow lights for stadiums enables turf managers to have a climate-controlled environment coupled with a carbon dioxide canopy to further promote turf growth.
The introduction of these could well be a game-changer for Venue management, leading to reductions in turf replacement costs and the production of higher quality surfaces. These have significantly lower running costs compared to HPS light rigs. The results have been nothing short of amazing as shown in the images below which were all taken 24-48 hours.
These turf grow lights offer:
- Variable light spectrum ranging allowing exceptional flexibility to promote top and/or root growth.
- These have an inbuilt irrigation system.
- Each unit has a carbon dioxide canopy to further promote growth. Rates of up to 10mm in shoot and root growth can be achieved in 24 hours.
- In built heaters. The image below was taken when the canopy temperature was 31°C compared to a surrounding temperature of approximately 12°C.
- Their high maneuverability means that two people can easily move them.
Turf grow lights: LED vs HID
Since their invention in the early 1700s, High-Intensity Discharge (HID) lights have become the dominant technology in turf grow lights. These lights put out huge amounts of light and their spectrum is close enough to the sun to promote plant growth.
However, LEDs are well-positioned to take over the leading role in this market. HID bulbs are categorized based on the gas that is used in them. The two main types are high-pressure sodium (HPS) and metal halide (MH) lights. The type of gas used in the bulb determines the colour spectrum and wavelength. Typically, HPS lights are used in the SGL and MLR turf grow lights (http://sglconcept.com https://mlrsports.com ) found at the MCG, and Accord Stadium are more towards the red and orange hue. In contrast an MH bulb produces a blueish color, which is useful for the vegetative phase.
Using light for plant health – The SeeGrow® approach.
LED turf grow lights are manufactured by UK-based SeeGrow® Developments with outstanding results being achieved of up to 10mm growth in 24 hours of leaf and root. SeeGrow has approached the issue of meeting the specific requirements of turf by utilizing a light spectrum that is tailored to meet the needs of the turf present. These are turf-specific lights rather than simply retro-fitting horticultural lights.
One of the main advantages of LED over HPS and MH lights is the adjustable light spectrum. They are now being used at Manchester City, Juventus, The San Siro, Tokyo Stadium, Chelsea FC, and Wembley Stadium.
The introduction of high-power LED systems could well spell the end of HPS dominance for several reasons:
- LED grow lights last six times as long as HPS.
- Their directional lighting requires no reflectors.
- LED grow lighting uses no toxic metals.
- Energy savings range from 50%-70% over HID lights.
- No cooling is necessary as they do not burn turf.
- Maximum chlorophyll absorption.
- Less frequent watering.
- Bias on desired spectrum possible by dimming.
- Due to the 2-3 times efficiency per m2 in comparison to HPS, less pitch treatment in operational hours and/or lesser equipment is required.
- Savings on carbon footprint – 9 HPS rigs each containing 60 lamps by 2,000 (seasonal) operational hours produce 800 tonnes of CO2 (800,000 kg). By using LED, savings are to be obtained varying from 200 to nearly 400% on CO2 emissions.
A ‘’light’’ refresher course! Daily Light Intergral (DLI)
Just to refresh your memory, DLI is the cumulative amount of photosynthetic light that is received each day. The DLI is measured as the number of moles of light (mol) per square meter (m-2) per day (d-1), or mol·m-2·d-1. The DLI can have a profound effect on root and shoot growth. Variations occur in DLI between C3 and C4 grasses and also between different cultivars
PAR (Photosynthetically Active Radiation) is a region of the electromagnetic spectrum (400 to 700 nm) that promotes photosynthesis.
PPF (Photosynthetic Photon Flux) tells us how much PAR a light source emits. PPF does not measure PAR, but it tells you how many photons within the PAR region are coming out of the light source every second.
PPFD (Photosynthetic Photon Flux Density) measures the number of photons within the PAR region every second. If you have a PAR meter, it is reporting PPFD (μmol/m2/s) measurements.
So what are the key differences between HID and LED lights?
LED turf grow lights last six times as long:
The output of HID lamps can degrade as much as 10-15% after only one year. As HPS lights degrade, the spectrum shifts toward the Green/Yellow range, which is poorly utilized by plants. LEDs last for at least 50,000 hours with less than a 10% drop in output with little or no shift in the spectrum.
LED directional lighting requires no reflectors.
The process of creating light with HID lamps is extremely efficient, with HPS lamps running as high as 1.7umol/j (#photons out / joules of energy in). However, directing that light down to the area where it will be used is not so efficient, as it requires a reflector. The very best reflective materials used run around 95% total reflectivity. This means that every time light strikes that surface, 95% reflects off and 5% absorbs and is converted to heat.
With a large diffused light source like an HID lamp, it often can be many reflections, and with each reflection, you lose at least 5%. Even the best HID fixtures typically have an overall fixture efficiency of 85% or less. That means a 1.7 mmol/joule rating of a DE HPS lamp is effectively 1.45mmol/joules when directed towards the canopy. Since LEDs are directional they do not require reflectors.
LED turf grow lights use no toxic metals.
LED (Light Emitting Diode) is a solid-state semiconductor device that can convert electrical energy into visible light directly.
Energy savings range from 50%-70% over HID lights.
HPS lights are quite efficient producing over 100 lumens per watt. However, when we consider LEDs, light output exceeds 300 lumens per watt. As the image below shows LEDs are showing ever-increasing efficiencies.
No cooling necessary and consequently no turf burn.
HID Lamps have an interior wall temperature around 700°C. LEDs typically emit 50% less heat compared to HIDs.
HID’s fixed spectrum output – not ideal for turf.
Turf absorb light and use the photons energy to strip the hydrogen out of water and combine it with the carbon from the Carbon Dioxide in the air (plus relatively small amounts of soil minerals) to create plant matter. They have several pigments that can absorb light and fuel plant processes, but far and away the most prevalent and efficient pigment for photosynthesis is Chlorophyll.
Spectrum and Photosynthesis.
In using light plants convert incoming light into chemical energy by using chlorophyll in leaves to absorb only the blue and red wavelength portions of the electromagnetic spectrum.
How do plants use light?
The key to using lights for plant health is to know how the turf uses it! As the above shows, there are two forms of Chlorophyll (Chlorophyll A and Chlorophyll B). Each has absorption peaks in both the Red and Blue spectrums, and both reflect yellow and green, (hence plants green color,). While the green/yellow bands can be absorbed by other pigments, over 50% of this spectrum range is reflected away and/or poorly utilized.
Blue light (400 to 500 nm).
Blue light helps regulate the opening of stomata and acts to inhibit etiolated growth. Turf grown under blue light has smaller leaves and shorter stems. Many LEDs for plant applications emit at least a small amount (such as 10-20 percent) of blue light.
Green light (500 to 600 nm).
Plants appear green because they reflect and transmit slightly more green light than they do blue or red light. Chlorophyll also absorbs green light poorly. Green light is sometimes stated as not being useful to plants for photosynthesis. However, it is still moderately effective since other pigments absorb the light and make it useful for photosynthesis.
Red light (600 to 700 nm).
Most LED arrays emit a high percentage (often 75-90 percent) of red light because it is absorbed well by chlorophyll. Red light is considered the most efficient waveband for photosynthesis, but turf can become etioliated in the absence of other light wavelengths. The graph below shows plant absorption throughout the PAR spectrum range. Absorption around the green/yellow boundary is as low as 30% and from 620 (range/red boundary) to 520 (Blue/Green boundary) is completely under 50%. Other less efficient pigments can absorb and utilize this spectrum range.
Metal Halide differs from HPS in the fact that the spectrum bands are generated by individual Metal Halides. These turn to gas and emit light when heated. Metal Halide lamps have traditionally favoured the blue end of the spectrum. As the lamp light gets “warmer” in colour and generates more red they get less efficient, more expensive, and degrade faster. And as you can see from the graphs they still produce minimal amounts of far red at the critical 675nm Chlorophyll A peak.
LEDs are the only lighting technology that can be designed to meet specific light spectrums for plants.
The graph below shows a typical HPS spectrum. You can see from these graphs that the majority of the HPS spectrum actually falls in the region of lowest plant absorption.
Individual LED chips produce very narrow spectrum bands, so LED turf grow lights can be precisely mixed to deliver a spectrum that is optimized for maximum plant absorption and utilization. And it is this ability to deliver exactly those frequencies the plant uses best, and all at very high efficiencies, with 30-40% less input power.
Different spectrum can have a major impact on specific plant morphology (changes in plant characteristics such as leaf and stem size, plant shape, etc..) and this is referred to as “Photomorphogenesis.” The main influencer on this is the ratio of Red: Far red light. Under normal light conditions, the R:FR ratio is usually constant all year round, averaging about 1.15 (Smith, 1982). However, R:FR ratio could drop to as low as 0.7 at dusk. One aspect of Photomorphogenesis that has significant research support is the shade stretch response. Shade light has a higher proportion of Far Red (FR) than is found in direct sun, so If the ratio of Red (R) to Far Red(FR) falls below a certain threshold (such as under trees or in shade), turf will begin to stretch and become etoliated, and exhibit a reduction in chlorophyll content and leaf thickness.