Marijuana Grow Lights
LED grow lights – More detail
HID grow lights – More detail
High pressure sodium (HPS) grow lights – More detail
Metal halide (MH) grow lights – More detail
Fluorescent (CFL) grow lights – More detail
Grow light reflectors – More detail
Marijuana grow lighting basics
We will take a look at the specific light required by marijuana for growing purposes. Let’s start with a bit of light measurement; nanometres (nm) are a measurement of one specific wavelength of light (one specific color). While Kelvin (°K) which is discussed in more detail later on, rates the ‘temperature’ of a light and offers an indication to the peak nanometers (nm) within the spectrum that each light offers.
The formula between Kevin and nanometres; 2,897,768 / K = nanometres (nm) however the two do not relate perfectly and this can only be used as a guide as to where a light source might actually be peaking in a precise nanometer (nm). Remember each the light source will offer a spectrum measured in nanometres (nm), say 500 to 700 nm.
Light in nanometres
Generally visible light is discussed in terms of wavelengths (rather than frequencies) using the unit nanometers (nm) where 1 nm = 1 billionth of a metre. Humans recognize these wavelengths as different colors starting at approximately 380 nm as the shortest wavelength within violet light and 750 nm as the longest wavelength within red light.
Marijuana plants need light from the right part of the spectrum with the right amount of intensity to encourage proper yet fast growth. Cannabis plants respond principally to light from the blue end of the spectrum for vegetative growth and from the yellow, amber, red end for root growth and flowering.
- The image above outlines the entire spectrum of visible light in nanometres (nm);
- Point (A) in the blue spectrum indicates is the light spectrum that marijuana plants require for vegetative growth;
- Point (B) outlines the yellow, amber and red spectrums which are required for pre-flowering and flowering (budding).
Growing marijuana will use the light from 400 through to 700 nanometres (nm) which will cover ‘chlorophyll a’, ‘chlorophyll b’ and photosynthesis production which is known as the Photosynthetically Active Range, or PAR for short.
HPS lights offer light in the spectrum from approximately 540 through to 700 nm, typically yellow, amber and red light. While the MH lights offer light from approximately the 350 to 550 nanometres (nm) in the blue, green to yellow range. However it always depends on what brand lamp your purchase as some HPS lamps are ‘cooler’ and some MH lamps a bit ‘warmer’. LEDs need to be mixed together, some blues, some reds, etc to create good broad spectrum LED grow lights, these are the new breed of grow light that cover the full grow range from 400 through 700 nm.
Light in terms of Kelvin (°K)
We can see from the scale below how different light sources hit the Kelvin (°K) scale at different places. The lower the degree K, the more “warm”, or red the light appears. The higher the degree K, the bluer, or “cooler” the lamp appears. Kelvin is a scientific term; Kelvin temperature measures the color of a light source relative to a black background.
In simpler terms, it is the average degree of warmth or coolness of a light source, not with regards to the physical temperature, rather to the visual temperature of the light.
Depending on which metal halide (MH) grow light you use they have an average of 3,200 to 5,500 °K while high pressure sodium (HPS) grow lights have an average of 2,200 °K and broad spectrum LEDs use a number of different LEDs in a mix, some are in the blues, some in the reds and some in between.
All light has a wavelength, frequency and speed. Some light is visible and some like infrared invisible to the naked eye, below are a couple of terms that get thrown around while you look for your next grow light, it’s worth knowing them.
Candela – This is the unit of luminous intensity with one candela.
Efficacy of a light source – This measure lets us know just how efficient a light source is and is simple maths to work out. Total light output divided by the power input (Watts) = lumens per Watt.
Foot-candle – The Imperial measure of how intense your light is ie how much light is received by 1 square foot of any surface situated 1 foot from the light source of 1 candle.
Lux – The metric unit of measure for luminance of a surface. Therefore one lux is = to one lumen per sq meter or 0.0929 foot-candles.
Lumen – This is the unit of light flow which is also known as luminous flux. All lights
can be measured to a total lumen output. Light fixtures can be expressed in lumens and usually the lamp will lose intensity (lumens) as it gets older.
The more right light marijuana plants receive, the faster and stronger they will grow.
Grow light setups
Growing your marijuana plants indoors means that you will be in charge of meeting all their light requirements. There are a variety of artificial grow lights on the market which work well, albeit to different degrees.
- Method 1 – Either MH or a HPS light through both stages of growth (good);
- Method 2 – Run a MH light through the vegetative phase of growth followed by HPS light through flowering (very good);
- Method 3 – Run both MH and HPS light through all phases of growth (very good);
- Method 4 – Run a broad spectrum LED system from seed to flower and they run cool and save electricity versus ‘Method 3’ (excellent).
Grow lights on the market
(1) Broad spectrum LEDs;
(2) Metal halides (MH);
(3) High pressure sodium (HPS);
(4) Compact fluorescent (CFL).
Broad spectrum LED grow lights
LED grow lights (light emitting diode) are not new but the broad spectrum models are new, and they work brilliantly.
LEDs were first introduced into electronics in 1962 and it should be no surprise that after 50 years those science boffins have had enough time to tweak them so that they are now commonplace in car headlights, traffic lights and hydroponic growing. High intensity discharge (HID) lamps such as metal halide (MH) and high pressure sodium (HPS) also work well but they are extremely wasteful in turning electricity into light with a vast amount of electricity turned into unwanted heat. LEDs are so efficient they use up to 80% less power than an equivalent HID because they create pure light instead of wasting electricity on heat.
Broad spectrum LEDs that operate around throughout the 450 to 700 nm light spectrum are perfect to use from seed to harvest. They carry the blue light for vegging and the yellow, amber, orange and reds for flowering. You can swap a 1000 Watt HPS for around 185 Watts of LED which would grow 16 plants with great results.
Good fan-less LEDs run 1W bulbs and can be situated mere inches above the canopy, however setting them at around 18 inches allows the lights to disperse the light over a larger area and gets better results. You can buy 2W and 3 W LEDs, however please note that these are using the same bulbs as the 1W versions but just have more current running through them. We hear that these 2W 3W and sometimes 5W LEDs are more prone to fail as the LEDs were originally built as 1W types but through testing they managed to squeeze more out of them with more current. These types of LEDs will also create some heat issues and usually operate with fans, yet another piece of equipment that can fail. It is best in the long term to aim for the safer, cooler 1W no fan varieties.
LEDs are now cheaper to run in the long term when compared to HIDs. Using LEDs instead of HIDs will lower your power bill, save you space, dramatically reduce heat, plus you can ditch the ballasts and reflectors. LED grow lights are of course also an excellent idea for the small, discreet grow room. Read more detail about LED grow lights.
HID (High intensity discharge) marijuana lighting
Although LEDs are a better bet and save you money in the long term they do cost more for an initial setup and if you just want to have a bash at growing some marijuana at home then maybe a cheap HID setup is more your style. There are two types of HID grow lights used for growing marijuana, metal halide (MH) and high pressure sodium (HPS).
Due to the heat that is emitted from these intense types of fixtures, you should hang them according to size. Smaller wattage systems (100 W and 250 W) should be hung about 2 to 3 feet from the top of the plants. Medium wattage systems (400 W and 600 W) should be hung around 4 feet from the top of the plants. High wattage systems (1000 W and up) should be placed at least 4 to 6 feet from the plant tops. More detail on HID grow lights.
Metal halide (MH) grow lights
Metal halide bulbs produce an abundance of light in the blue spectrum. This color light promotes plant growth and is excellent for green leafy growth and keeping plants compact. Other than LEDs we feel they are still one of the best types of light to be used as a primary light source (if no or little natural sunlight is available) but depending on the brand you may lack important amber and red light required for flowering. More detail on MH grow lights.
High pressure sodium (HPS) grow lights
High pressure sodium (HPS) bulbs emit an orange-red glow and are deficient in the blue spectrum. This band of light triggers hormones in plants to increase flowering/ budding in plants. They are one of the best lights available for secondary or supplemental lighting (used in conjunction with natural sunlight or MHs). Using this as a sole point of light is only recommend for greenhouse growing applications. More detail on HPS grow lights.
Fluorescent and compact fluorescent (CFL) grow lights
This type of light is perfect for starts and seedlings. They are also popular for growing low-light plants like herbs and African violets. Fluorescent lights are low intensity and need to be placed within 8” (up to 15” for shade loving plants) of the plants to be effective. They are generally a poor light source for flowering and budding primarily because of their low lumen output. Read about the new CFL grow lights. Like LEDs and CFLs incandescent lights are also good for starting germination and seedlings They are not very good at all for the vegetative growth or flowering stages because of their low lumen output and limited range.
Costs of running marijuana lighting systems
To calculate your daily electricity cost you need to add up the total Watts for each part of the grow system; lights, ballast, fans and pumps etc. Take the grow lights and other electrical equipment’s combined Wattage, and divide it by 1,000 to find the number of kilowatts (kWh) used per hour. Then multiply that number by the amount your electric company charges per kilowatt hour (kWh).
Example; HID lights will use the number of Watts it emits per hour, i.e.; 600W system will use 600 Watts per hour (regardless of spectrum) and that is 0.6 kilowatts, make sure you include 100W to 150W for each ballast used so that HID 600 Watt HID is really sucking down say 700 Watts per hour. So if your electric company charges you $0.20 per kilowatt hour this lamp will cost 0.7 X $0.20 = $0.14 per hour to run. Multiply that out for a daily or monthly cost per lamp. LED grow lights run at about 1/8 of these rates.
Optimal light height (OLH)
- LEDs – around 12 to 18 inches from the top of the plants;
- 400w HPS – 18 inches;
- 600w HPS: 18 inches;
- 1000w HPS: 24 inches.
Vegetative grow light timing
After seed germination your plant will move into the vegetative growth phase known as the ‘photoperiod’ which is the direct relationship that your plants have with the hours of light and darkness offered to them.
With control over the amount of light your plants receive you can effectively dictate their grow cycle. You can replicate vegetative growth by using a timer to have your lights on between 18 and 24 hours and off with darkness for the remaining period; between 6 and 0 hours every day. More information on pruning during vegetative growth.
HPS lights are not as active in the blue / green light spectrum required for active vegging and although MH lights are they can be quite harsh to the young seedlings primarily due to their heat generation. If you plan to use HPS lights later on then we suggest starting out with CFL’s or LEDs to let your seedlings build up to stark heat given off by MH and HPS lights. Think about nature where the seeds would germinate in spring when the sun is not as strong as it will be in summer, it is best to try and replicate that.
An alternative to growing under HPS or MH during vegetation is to set up a vegetative area, and a flowering area. The vegetative area would use a cloner or something similar that would allow seeds or clones to grow under lights 24 hours a day.
Induce marijuana flowering (budding) timing
In their natural environment plants begin to flower as the days shorten at the end of summer and start of fall. To induce flowering (budding) you need to switch the light cycle to 12 hours of light and 12 hours of darkness for during every 24 hours.
When you make this change is up to you but it’s best after the plant has had some time to get from 12 to 20 inches tall. Forcing plants to flower when they are quite small increases crop rotation and overall yield. By doing this you will be able to fit more plants under your lamps which is what the Dutch concepts ‘Sea of Green’ or ‘Screen of Green’ replicate. If you are limited by the number of marijuana seeds, clones or viable cuttings that you have you may wish to wait until the plants are bigger so that you get more buds per individual plant.
Once you have induced flowering you will see changes in your plant within one to two weeks, it is imperative to remove the male plants. Read how to do that and more about marijuana flowering here.
While the flowering plants are going through their cycle with the hydroponic set up, you can germinate other seeds or clones and get them ready for the next cycle. New seedlings or clones can then be started in the cloner.
Since the flowering plants need absolute darkness during the dark phase, the light from the vegetative area can’t reach the flowering plants. So they need to be isolated, either by using curtains or put in separate rooms.
Technical lighting basics
Let’s get into the more technical side of lighting as it is useful to know what you are actually doing. There is no point in buying the wrong lights.
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