Before considering which LED Growth Light to use, it will be good to know the following points for you to make the right decision for your plant.
Color Spectrum
Sunlight, as we know, is critical for the survivability of the plant. Sunlight itself contains the colour spectrum of a rainbow and when these colours are mixed together, we consider them to be white light or yellowish white light.
In specification terms, we use wavelength numbers to refer to the specific colours instead of its name. So a red colour would mean in the wavelength number of 630 or 660. In our own optic perspective , it still looks red to us but in actuality, it is of a different tone of red.
With the advancement in LED Technology, we are able to tune and set the wavelength number to the desired colour to be emitted which will give the plant the optimal wavelength range for it to grow.
Different Colour, Different Purpose
With the correct amount of light, its colour allows photosynthesis to occur in plants and this is done with the specific chemical in the leaves. Research done by NASA has the following finding that provides the basis of LED light recipe for plant growth:
Red Light (630 – 660 nm)
Essential for the growth of stems, as well as the expansion of leaves. This wavelength also regulates flowering, dormancy periods, and seed germination.
Blue Light (400 – 520 nm)
Needs to be carefully mixed with light in other spectra since overexposure to light in this wavelength may stunt the growth of certain plant species. Light in the blue range also affects the chlorophyll content present in the plant as well as leaf thickness.
Green Light (500 – 600 nm)
Penetrates through thick top canopies to support the leaves in the lower canopy.
Far Red Light (720 – 740 nm)
Also passes through dense upper canopies to support the growth of leaves located lower on the plants. In addition, exposure to IR light reduces the time a plant needs to flower. Another benefit of far red light is that plants exposed to this wavelength tend to produce larger leaves than those not exposed to light in this spectrum.
Source: Advanced LED Lights (All Articles, Technology, 2016-12-17)
SUN – LIKE Spectrum ( 4000K – 5000K CCT ) – Seoul
Semiconductor announced the results of a series of experiments that demonstrated a higher growth rate and higher flavonol (a type of antioxidant) content in crops grown under SunLike Series natural spectrum LEDs than those grown under standard white LEDs. SUN – LIKE Spectrum is best for the growth of Leafy greens, like lettuce and herbs.
Intensity vs PAR.
In the lighting terms, lumen intensity level is commonly used to measure the total quantity of the light emitting out from the source at all direction. But when in comes to lighting for the plants, it is more important to know how much of the light reaches the plant.
The PAR (Photosynthetic Active Radiation) is the measurement that gives us the most useful information for comparing grow lights. It is also referring to the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drives photosynthesis. The recommended units of measurement for PAR, µmol m-2s-1.
What is PPF & PPFD?
The amount of PAR emitted over a period of time will be provided as Photosynthetic Photon Flux (PPF) of that light. This is referred to the number of moles of photons expressed within the 400-700nm over time, in umol/s.
PPFD, also known as, Photosynthetic Photon Flux Density is the measurement of the amount of PAR that actually reaches the plant. In a more technical term, it will be the number of Photosynthetically Active Photons (PAR) that falls on a given surface every second. The unit-micromoles per square meter per second (μmol/m2/s).
When it comes to PPFD (Photosynthetic Photon Flux Density) calculation, the height and the designated area size is important to be factored in. In general, each different type / species of plant has specific and unique PPFD requirements in order to get the best yield and growth . For example, flowering plants need about 300 – 600 umols PPFD during the vegetative phase and 800 – 1000 umols PPFD during flowering.
The Daily Light Integral (DLI)
The Daily Light Integral refers to the measurement in moles per m2 per day, showing the total number of photosynthetically active photons each day. In other words, having the higher PPFD over short period vs lower PPFD over longer period has the equivalent DLI.
Having PPFD for a longer period doesn’t mean it is good for the plant. Plants still require a “no-light” period to process the carbon-based molecules created during the photosynthesis. Some plants will require 6 hours of darkness during their vegetation phase and going for 12 hours of darkness when it comes to flowering phase.
In all, a minimum DLI is necessary for the proper growth for the plan. Prolonged lighting may cause bleaching and leaf burn. With reference to the nature, the DLI on the surface of our planet can range from 5 to 60 mol/m2/d depending on the time of year and the duration of the day.
Therefore, it is good to time the program so that it can incorporate with the LED Growth Light and set the photoperiod for the different phases on the plant growth. E.g. 18 hours for vegetation phase and 12 hours for flowering phase.