LED Grow Lights – Do’s and Don’ts
First, when it comes to growing with LED lights it’s important to know what the light you are using is made of. The wattage of LED, the angle of the lens, and the total wattage consumed by the light. These factors paired with the intensity of the light will determine the best method to follow when using your new LED grow light.
Determining Color and Power of LED Grow Lights
Let’s start with the type of plant and light intensity you desire first. Vegetative types of plants like lettuce or spinach do not need as much intense light to grow. If you are growing flowering and fruiting plants you will need a very intense light with a strong emphasis on red colors. Flowering plants can be hard to grow with LED grow lights if the light uses very cheap 1w LEDs and a wide angle lens (120 degrees) which makes the light spread out and drastically reduce the intensity of the light. Flowering plants should have as much light as possible and usually do much better under all 3w LEDs with a 90 degree lens. With this type of high intensity LED grow light, flowering plants are grown best with the light hung about 18 inches above the plant canopy.
If you have cheap low wattage 1w LEDs with the traditional 120 degree lens you will want to hang the light no higher than 6 inches above the plant canopy in order to produce results. If you have less than 1w/LED of in your lights then I would suggest only using them for vegetative growth, seedlings and clone transplants. These cheap low wattage LED grow lights are not all they are claimed to be and usually will result in a frustrated grower with little to show for a harvest.
Using Light Movers with LED Grow Lights
Another factor in growing with LED grow lights is side light and light movers. LED grow lights are directional lights that focus their light in one direction. If you add some florescent lights to the side of your garden you can see proportional benefits in harvest without much of an increase in your wattage or cost per unit of harvest. Light movers with high powered LED grow lights work great to increase the number of leaf sites that receive intense light and will allow your plants to fill out more evenly. Remember though to check your lights specifications regardless of side lights and light movers because if your wattage or lens angle is weak you will need to be much closer or not use those cheap lights on your flowers at all.
Rated 3w LED Grow Lights
If you are looking for a great place to find high intensity LED grow lights with all 3w LEDs and 90 degree lens angles then check out ledgrowlight-hydro.com, they also sell many custom made LED grow lights to add certain colors to your garden.
LED Aquarium Light Intensity
Engineering advances in both LED and associated lens technologies have resulted in some rather amazing breakthroughs and these are becoming available to consumer markets. The LEDs used by AI are among the ‘brightest’ available. See Figures 9 and 10 for details.
Figure 9. The light produced by the Aqua Illumination LED array is quantifiably ‘bright.’ Note the distance of the PAR sensor from the luminaire (5”) – holding the sensor closer to the luminaire saturated the sensor. In other words, the LEDs produced more light than the sensor could measure (1,999 µmol·m²·sec – the intensity of sunlight at noon on a cloudless day).
Figure 10. Light intensity you would see at a water depth of 14.25” in an aquarium. The luminaire is about 1” above the water surface (with the supplied legs removed).
Light Production: LED versus Metal Halide
How does the AI LED array’s light intensity compare to that of a ‘traditional’ light source (such as a high Kelvin metal halide lamp)? An XM 250-watt 20,000K metal halide’s light output (PAR) was compared to that of the AI LED luminaire (see ‘Methods’ for details). In a nutshell, the LED array out-performed the 250-watt metal halide.
Figure 11. Light intensity (Photosynthetically Active Radiation, or PAR, reported in units of micromol photons per square meter per second) of a metal halide lamp. Compare these numbers to those in Figure 9.
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Photosynthetically Usable Radiation
Photosynthetically Usable Radiation (PUR) is an important, but not an ultimate, concept. PUR differs from PAR (Photosynthetically Active Radiation) in that PUR considers not just light intensity, but also the spectral composition of light. In order to estimate PUR, we have to consider which portions of the visible spectrum are actually absorbed by zooxanthellae. Fortunately, researchers have determined this, and call it an ‘action spectrum.’ An action spectrum describes the relative effectiveness of energy at different wavelengths in producing particular biochemical or biological responses (such as oxygen evolution, carbon uptake, electron transport rate, etc., during photosynthesis). Hence, or our purposes, we will consider PUR as those wavelengths falling between 400-550nm (absorption bandwidth of chlorophylls a, c², and peridinin) and ~620-700nm (red absorption bandwidth of chlorophylls a and c²). Figure 12 demonstrates the action spectrum of zooxanthellae isolated from the stony coral Favia.
Using these ranges, 74.7% of PAR produced by the AI unit is actually PUR and is therefore light usable by zooxanthellae and plants. It should be noted that light not absorbed by photopigments and the coral animal is reflected and results in our visual perception of ‘color.’ I think most hobbyists will likely prefer a visually-pleasing light over a photosynthetically-efficient light (which would appear reddish-blue in color).
My point is that we, as hobbyists, shouldn’t get carried away with this concept and PUR is more of a factor in low-light (photosynthetically sub-saturating) intensities.
Figure 12. Zooxanthellae and their photopigments ‘prefer’ certain light wavelengths for photosynthesis.
An in-depth discussion of PUR and its relation to photosynthesis under conditions of photosynthetically sub-saturating and saturating light intensities is well beyond the scope of this article. However, it does deserve attention and will be the subject of a future article.
