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Growing info

Growing info

We always advise against breaking the laws where you live, in the UK we'd like to remind you of ; MISUSE OF DRUGS ACT 1971 By section 6 of the Misuse of Drugs Act 1971 it is an offence to cultivate any plant of the genus Cannabis in the United Kingdom without a license from the Secretary of State. Anyone committing an offense contrary to this section may be imprisoned or fined, or both. Visitors to this website are advised against breaking the law

Learn how to grow weed with easy step by step grow guide complete with pictures and videos there is the ton of information for new growers.

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Light Absorption for Photosynthesis

Photosynthesis depends upon the absorption of light by pigments in the leaves of plants. The most important of these is chlorophyll-a, but there are several accessory pigments that also contribute.

The measured rate of photosynthesis as a function of absorbed wavelength correlates well with the absorption frequencies of chlorophyll a, but makes it evident that there are some other contributors to the absorption.

The plot of the absorption spectra of the chlorophylls plus beta carotene correlates well with the observed photosynthetic output. The measure of photochemical efficiency is made by meauring the amount of oxygen produced by leaves following exposure to various wavelengths.

It is evident from these absorption and output plots that only the red and blue ends of the visible part of the electromagnetic spectrum are used by plants in photosynthesis. The reflection and transmission of the middle of the spectrum gives the leaves their green visual color. 

led grow lights

 

Color spectrum[edit]

 
The color temperatures of different grow lights

Different grow lights produce different spectrums of light. Plant growth patterns can respond to the color spectrum of light, a process completely separate from photosynthesis known as photomorphogenesis.[27]

Natural daylight has a high color temperature (approximately 5000-5800 K). Visible light color varies according to the weather and the angle of the Sun, and specific quantities of light (measured in lumens) stimulate photosynthesis. Distance from the sun has little effect on seasonal changes in the quality and quantity of light and the resulting plant behavior during those seasons. The axis of the Earth is not perpendicular to the plane of its orbit around the sun. During half of the year the north pole is tilted towards sun so the northern hemisphere gets nearly direct sunlight and the southern hemisphere gets oblique sunlight that must travel through more atmosphere before it reaches the Earth's surface. In the other half of the year, this is reversed. The color spectrum of light that the sun emits does not change, only the quantity (more during the summer and less in winter) and quality of overall light reaching the Earth's surface. Some supplemental LED grow lights in vertical greenhouses produce a combination of only red and blue wavelengths.[28] The color rendering index allows comparison of how closely the light matches the natural color of regular sunlight.

The ability of a plant to absorb light varies with species and environment, however, the general measurement for the light quality as it affects plants is the PAR value, or Photosynthetically Active Radiation.

There have been several experiments using LEDs to grow plants, and it has been shown that plants need both red and blue light for healthy growth. From experiments it has been consistently found that plants grown under only red (660 nm) LEDs grow poorly with leaf deformities, though adding a small amount of blue allows most plants to grow normally.[23]

Several reports suggest that a minimum blue light requirement of 15-30 µmol·m–2·s–1 is necessary for normal development in several plant species.[29][30][31]

 
LED panel light source used in an experiment on potato plant growth by NASA

Many studies indicate that even with blue light added to red LEDs, plant growth is still better under white light, or light supplemented with green.[23][24][25] Neil C Yorio demonstrated that by adding 10% blue light (400 to 500 nm) to the red light (660 nm) in LEDs, certain plants like lettuce[20] and wheat[21] grow normally, producing the same dry weight as control plants grown under full spectrum light. However, other plants like radish and spinach grow poorly, and although they did better under 10% blue light than red-only light, they still produced significantly lower dry weights compared to control plants under a full spectrum light. Yorio speculates there may be additional spectra of light that some plants need for optimal growth.[20]

Greg D. Goins examined the growth and seed yield of Arabidopsis plants grown from seed to seed under red LED lights with 0%, 1%, or 10% blue spectrum light. Arabidopsis plants grown under only red LEDS alone produced seeds, but had unhealthy leaves, and plants took twice as long to start flowering compared to the other plants in the experiment that had access to blue light. Plants grown with 10% blue light produced half the seeds of those grown under full spectrum, and those with 0% or 1% blue light produced one-tenth the seeds of the full spectrum plants. The seeds all germinated at a high rate under all light types tested.[22]

Hyeon-Hye Kim demonstrated that the addition of 24% green light (500-600 nm) to red and blue LEDs enhanced the growth of lettuce plants. These RGB treated plants not only produced higher dry and wet weight and greater leaf area than plants grown under just red and blue LEDs, they also produced more than control plants grown under cool white fluorescent lamps, which are the typical standard for full spectrum light in plant research.[24][25] She reported that the addition of green light also makes it easier to see if the plant is healthy since leaves appear green and normal. However, giving nearly all green light (86%) to lettuce produced lower yields than all the other groups.[24]

The National Aeronautics and Space Administration’s (NASA) Biological Sciences research group has concluded that light sources consisting of more than 50% green cause reductions in plant growth, whereas combinations including up to 24% green enhance growth for some species.[32] Green light has been shown to affect plant processes via both cryptochrome-dependent and cryptochrome-independent means. Generally, the effects of green light are the opposite of those directed by red and blue wavebands, and it's spectulated that green light works in orchestration with red and blue.[33]

Light requirements of plants[edit]

A plant's specific needs determine which lighting is most appropriate for optimum growth; artificial light must mimic the natural light to which the plant is best adapted. If a plant does not get enough light, it will not grow, regardless of other conditions. For example, vegetables grow best in full sunlight, and to flourish indoors they need equally high light levels, whereas foliage plants (e.g. Philodendron) grow in full shade and can grow normally with much lower light levels.

Photoperiodism[edit]

In addition, many plants also require both dark and light periods, an effect known as photoperiodism, to trigger flowering. Therefore, lights may be turned on or off at set times. The optimum photo/dark period ratio depends on the species and variety of plant, as some prefer long days and short nights and others prefer the opposite or intermediate "day lengths".

Much emphasis is placed on photoperiod when discussing plant development. However, it is the number of hours of darkness that affects a plant’s response to day length.[34] In general, a “short-day” is one in which the photoperiod is no more than 12 hours. A “long-day” is one in which the photoperiod is no less than 14 hours. Short-day plants are those that flower when the day length is less than a critical duration. Long-day plants are those that only flower when the photoperiod is greater than a critical duration. Day-neutral plants are those that flower regardless of photoperiod.[35]

Plants that flower in response to photoperiod may have a facultative or obligate response. A facultative response means that a plant will eventually flower regardless of photoperiod, but will flower faster if grown under a particular photoperiod. An obligate response means that the plant will only flower if grown under a certain photoperiod.[36]

Photosynthetically Active Radiation (PAR)[edit]

Lux and lumen are photometric units, in that different wavelengths of light are weighted by the eye's response to them. This makes them inappropriate measure of the lighting level in a horticultural lighting system. Instead, lighting levels are quantified as amount of radiation in the wavelength range from 400 to 700 nm, or photosynthetically active radiation (PAR). It can be expressed in units of energy flux (W/m2) or photon flux (mol m−2s−1).

According to one manufacturer of grow lights, plants require light levels between 100 and 800 μmol m−2s−1.[37] For daylight-spectrum (5800 K) lamps, this would be equivalent to 5800 to 46,000 lm/m2.

Different grow lights have different PAR spectrums that can be compared against each other and to the sun:

PAR Sunlight Spectral Comparison
 
PAR vs Sunlight spectral comparison
Grow Light - PAR MH Spectral Comparison
 
PAR vs MH spectral comparison
Grow Light - PAR HPS Spectral Comparison
 
PAR vs HPS spectral comparison
Grow Light - PAR Fluorescent Spectral Comparison
 
PAR vs Fluorescent spectral comparison
Grow Light - PAR LED Spectral Comparison
 
PAR vs LED spectral comparison
 
grow light, grow lights, grow lighting
 
PAR vs High Efficiency Plasma
grow lighting
 
PAR vs LED spectral 

 

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