In our last article, Which Grow Light Should I Use, we discussed which factors should play a role in choosing between different grow lights, and what lights are best for flowering. We explained the pros and cons of high pressure sodium, metal halide, fluorescent and LED grow lights for growing cannabis. In this article we provide some basic information on how to get the best results with each type of light.
Let’s start off with fluorescent bulbs since they are probably the easiest category out of the bunch. We’ll mostly talk from a T5 grow light perspective, as these lights were designed to grow plants with. The name T5 stems from the diameter of the tube, which in this case is 5/8th of an inch. These tubes come in different lengths and many different colours. Regardless of our preferences, the information in this section is applicable for any type of fluorescent type you may choose.
The advantage of using fluorescent grow lights is they can literally touch the plants during both the growing and flowering stage without any catastrophes like you would experience with HID lighting. Fluorescent lights have much less issues with water and won’t have any problems if they get a little wet while switched on. T5 grow lights should stay between 10cm and 15cm away from the tops of the plants due to their low penetration and heat output. They can only penetrate the canopy down to about 60 centimetres, which is one of the reasons they are mostly used for vegetative growth. Another reason not to use fluorescent grow lights for the flowering phase is that yields can be very low, or at least very inefficient. Fluorescent grow lights usually only yield around 0,25-0,5g of dry bud per watt of electricity used. The final weight and biomass will suffer a great deal when compared to HID or LED lighting.
The spread given by fluorescent grow lights is generally quite horrible. This means that lights should be directly over your plants, so you’ll have to get some big lights if you intend to cover your entire canopy. You could do this by hanging a lot of CFL bulbs in strategic places, but is usually easiest to achieve using regular sized fluorescent tube lights. We prefer big, rectangular 4-tube T5 grow lights. Functionally there will not be much difference between brands, as fluorescent light revolves almost entirely around the bulbs themselves. Top brands for bulbs include Philips, GE and Osram. T5 fixtures are available from many different companies including well known brands like Hydrofarm, Apollo, Sun Blaze and Quantum.
As for bulbs you should make sure to get a bulb that is suitable for growing cannabis. Warm white lights (3000K colour temperature) are suitable for both growth and bloom, but will underperform compared to specialized horticultural tubes. These emphasize certain parts of the light spectrum to optimize plant growth. Vegetative growth is helped greatly by blue light, so this phase works best with fluorescent tubes with a 6400K colour temperature. Flowering relies more on red light, so 2800K bulbs are your best choice.
As stated in our previous article HID, but especially HPS, is the gold standard to which all other lights are compared. They produce intense light in a spectrum that fits the flowering phase very well, leading to reliable and potent yields.
The most efficient distance to keep an HID bulb above a canopy depends on the wattage of the light and your grow room conditions. You want your light close enough to provide energy to the plant, but far enough to avoid heat stress. A good rule of thumb is to make the distance between your lamp and canopy around 10cm (or 4in) per 100W. This would result in hanging a 600W light at a height of 60cm or a 1000W at 1m (3’ 8’’).
Of course the main reason not to hang a light too close is to avoid burning your plants, but this is not necessarily the most efficient. Additional ventilation or the use of a cool-tube reflector can allow you to position your lights closer. In terms of usable light, somewhere between 30 and 60cm is often more ideal as a lot of light is lost when put at a greater distance. A popular approach to test how close you can hang your lights is simply feeling it out. By holding your hand under your lights you can see how much heat they generate at different distances and adjust the height accordingly. The goal is to mimic outdoor circumstances, so if your light feels as hot as the sun does in the summer you’re probably on the right track.
Another important factor to keep in mind is coverage, which of course depends on how much distance there is between the light and plants. This is also affected by the reflective hood. Using a regular, cheap hood hung at an optimal height, HID bulbs of different wattages generally cover the following areas:
You can calculate the cost of electricity quite easily and this is probably something you should do before you start using HID bulbs. The calculations work the same for every type of light, but are usually more of an issue with HID lights as they use a lot of power. Calculations are often limited to the flowering phase, as the vegetative growth requires less light.
This is how you calculate the electricity cost of your grow:
Multiply the wattage of your light times the hours of light per day and divide that by 1000, this gives you the kWh per day. Multiply this number by the number of days your strain takes to flower and multiply the resulting number by your kWh price, which should be on your energy provider’s website.
Let’s calculate the costs for the flowering period of Moon Walker Kush, a strain with a 60 day flowering period, under a 600W HPS light, with electricity costing €0,20 per kWh:
12x600 = 7200 watt hours per day
7200/1000 = 7,2 kWh per day
60 x 7,2 = 432 kWh total
432 x 0,20 = 86,4
So a 60 flowering phase will cost you €86,40!
Most reasonably experienced growers yield around 1 gram of dry weight per watt using HPS grow lights and slightly less than that using MH. As you can see, this will generally be well worth the power bill.
HID bulbs come in single and double-ended versions, this means that they connect to your hood on one or both ends. Double ended bulbs are still relatively new in the indoor growing community, but have already been shown to be more effective than classic single ended bulbs. Double ended bulbs are more efficient in terms of energy, produce more intense light and last longer. The downside to all of this is that double ended hoods, ballasts and bulbs all cost substantially more than more classic HID setups. So far research by the Utah State University has backed up the claim that double ended bulbs are up to 30% more efficient than their single-ended counterparts. DE bulbs also lose less power over time, and will burn much brighter than single-ended bulbs after a lot of use. The price difference can be more than double though, which makes this a very personal choice.
HID lighting uses a ballast to run power to the light bulbs. The bulbs themselves are attached to the reflectors, these reflectors are also important but don’t play a role in the electrical story.
All ballasts fill the same role: they help start the light and regulate how much electricity the light receives. Without a ballast, a HID light would receive a too high voltage and explode. Ballasts limit the flow of electricity and give out heat in return. Ballasts also come in many different types, but these fall into one of two categories: digital (= electric) and other (usually magnetic). Each grow light must be paired with the correct ballast. A 400W HPS or MH needs a 400W ballast for example. A 1000W grow light requires a 1000W ballast and so on. In this day and age we recommend getting a digital ballast if you intend to use HID lights, as these have many advantages over older types of ballasts.
Digital ballasts have been developed to solve problems that older types of ballast came with, and to give the grower more control over their lights. The advancements with digital ballasts are:
Overall digital ballasts provide a ridiculous amount of advantages over standard ballasts, from being able to adjust light and power output, reduce noise and heat energy and even increase overall yields. With a price difference of only 50-100 euros, standard ballasts are simply not worth the hassle anymore.
Another important part of your HID lighting setup is the reflector. Because HID grow lights emit light in a 360° radius, most systems require some of the light to be bounced back in the right direction. There is not really a clear-cut choice, so make sure to consider your needs in terms of canopy size and height, as well as your ability to remove hot air.
While vertical growing is certainly an option, most growers tend to favour hanging a light over the top of their plants. In any case, you are trying to efficiently light up a certain canopy or grow space. Grow light manufacturers often refer to this as the “coverage” or “footprint” of a light. The angle of your reflector will dictate the spread of light, and to a lesser extent also the penetration. Wider hoods will cover a larger area with less penetration, whereas more focused hoods provide deeper penetration in a smaller area. Wider hoods can also be slightly closer to your plants, as the more diffuse light will also produce less concentrated heat.
This brings us to another important consideration to make when buying a reflective hood: how do you intend to deal with the heat your HID bulb produces? When buying an open hood, you should check if the distance between the bulb and the hood allows for enough air flow.
There are also closed, air cooled hoods that can be hooked up directly to your exhaust system. These hoods generally have an intake and exhaust hole for air and are sealed with a glass plate between your light and your plants. Air cooled hoods help reduce heat, but can also reduce your light output and thereby make your grow light less efficient. Exhausting air past your grow light also puts more strain on your exhaust system as the temperatures will be a lot higher.
The next thing you should look at is the material, which usually dictates the price. Most hoods are made of hammertone dimpled aluminum as this provides a very efficient reflective surface. Reflective materials are described with a “reflectivity index” number to indicate how much percent of the initial light is reflected. Materials with a higher reflectivity index are usually also sturdier and more expensive. Plain anodized aluminum for instance is cheap, has a reflectivity of around 70% and is prone to degradation. This won’t be as good as a high quality material like Physical Vapor Deposition (PVD) treated aluminum, which has a reflectivity index of around 95% and barely degrades at all.
A large part of deciding between reflectors is deciding how much money you want to spend on one. While we prefer more expensive, high-end reflective hoods ourselves we have also had good results with cheapers ones. In the grand scheme of things, a reflector is something you should probably save some money on if you are setting up for your first grow.
We’re big fans of the Adjust-A-Wing system, as these lights allow you to modify the angle of reflection during a grow. We prefer these over big air cooled hoods as they are more practical in terms of size and weight, offer more versatility and don’t lose any efficiency to a piece of glass.
In smaller spaces however, where height is an issue, air cooled hoods like those by Cool Tube are a great solution to any heat problems. You may lose a bit of light, but you’ll be able to use a stronger light than with a regular hood.
As a budget option we would like to include any simple hammer tone dimpled aluminum hood. We’ve found these for as cheap as 10 euros, which means any grower can afford these.
HPS grow lights come in many different types and configurations. Many of these are sold as complete packages, which is definitely something we recommend for newer growers. A complete HPS setup uses a reflective hood, ballast and a bulb, the latter is usually produced by separate companies. It is generally easier to use a reflective hood and ballast from the same company. We recommend the following companies if you’re looking for a regular HPS lighting setup:
For more efficiency but a higher investment we would suggest getting a double ended setup from Gavita or Dimlux, which are the current market leaders in Europe.
Bulb-wise, there are probably even more options than for other equipment. In Europe, Philips Son-T lights have been the industry standard for decades, but Osram (Sylvania) has always been a close second. Popular brands in the US include Hortilux and Lumatek products. Essentially HPS bulbs all do the same, but most brands try to optimize their bulbs by enhancing certain parts of the spectrum. This makes the lights more efficient but also more expensive, so deciding between bulbs is a very personal choice. The difference in yield between run of the mill HPS bulbs and their more “deluxe” counterparts is said to be around 10%, while the price difference can be more than threefold.
According to many, the future of grow lights is finally here, and it comes in shiny purple colours. LED grow lights are still developing rapidly and are therefore quite mixed in their results. The current standard for flowering is HPS lighting and in a perfect world LED lights would reach higher yields (per area) while using less energy and producing less heat and sound. In a more realistic world, we’re not completely there yet. LED lights are so open to modification that comparison between different models is difficult. A few years ago LED grow lights were still far inferior to HID lighting, but a lot has changed since. With some expert growers yielding almost 2 grams of dry bud per watt of lighting, LED lights are suddenly a very realistic alternative to HID.
LED lights work differently than other lights when it comes to light diffusion. A regular HID bulb radiates light into all directions, whereas an LED light focuses all of its light into a single direction. The exact direction and spread is determined by the lens, which is usually 90-120 degrees. In practical terms this means that you will not lose much intensity by hanging LED grow lights higher. We recommend a 90 degree lens angle unless you use your LED grow light to supplement other lights.
Some manufacturers advise keeping LED grow lights at the highest point in the grow tent for the entire grow. Most LED grow lights should be hung at a height of at least 60cm. Conventional grow lights encourage the grower to fight for a 30-60cm sweet spot, where the plants can absorb as much light as possible without suffering heat issues or wasting light. LED lights can be hung up to 2 metres away making canopy temperatures much easier to maintain. Good LED lights can yield over 1.5g per Watt of energy used.
Important benchmarks to keep an eye on are PAR, power consumption, type of diode, lens angle and the number of fans. PAR or photosynthetically active radiation is a direct statistic on how much usable light your plants are getting.
Diodes are complicated and can be made in many different ways from many different materials. For the general consumer it is important to remember that the colour of light, the amount of light emitted and the amount of power used are all determined by the diode. While the materials used etc. might get a bit too technical for the average user, make sure you pay attention to the watts.
The most common diodes are 3, 5 or 10W and come in single or double-chip versions. While higher may seem better, we recommend using 3W single-chip diodes as these are least likely to overheat and most likely to deliver what they promise.
Lower quality manufacturers often make their diodes use too much power, which makes them do well in lumen tests, but not so much in real world applications. So if a 3W diode uses less than 3 watts of energy, this is often a good thing. A major problem with cheaper LED grow lights is that it is often unclear if they are talking about the wattage of the diodes, or how much watts a light actually draws from the wall.
The type of diode will often dictate the description of a led light: manufacturers will call led lights with 50x3W 150W, but the same goes for 30x5W. This is where the power draw comes in, which is usually a much better way to compare lights.
Say we found two LED grow lights online for example:
This makes it likely that the light B, the “800W” light, is actually more powerful. Watch out for companies that are unwilling to state how many watts their products actually use, as they’re likely not completely honest about their diodes either.
There is also the often overlooked cooling system, which generally consists of heat sinks attached to the back of the diodes which are cooled by fans. While LED grow lights don’t produce much heat, it is very important to keep the diodes from overheating or they will burn out. Cheaper models can lack a bit of power in their fans, leading to a lot of noise and poor cooling. Unfortunately this type of information is often left out, so make sure to read some reviews before buying anything!
PAR, or photosynthetically active radiation, is the statistic for how much usable light your plants receive. In the case of growing cannabis, PAR is expressed in µmol/m2/s. This indicates the amount of usable light per square meter, per second. Most companies provide charts that indicate the average PAR at different distances from plants that can be used to hang your grow lights at an optimal height. You can also measure PAR using a PAR meter, which can tell you a lot about your grow light. In any case make sure your lights provide enough PAR for the flowering phase or your buds will stay light and fluffy.
Your plants will require more light as they grow, this can allow a grower to use less powerful grow lights for a large part of the grow. These are the general PAR recommendations we use for growing cannabis:
LED grow lights are very versatile and come in many different shapes and sizes. In this section we consider lights that are suitable for a full cycle of cannabis cultivation and provide the best bang for their buck, so to speak. Customer service is also an important point, as broken LED lights can often be fixed by simply replacing a few parts. Therefore we recommend buying your LED grow lights from companies that you know you can reach.
After some deliberation with an expert in the field of LED grow lights, we’re convinced that the Osram SMD SSL80 is by far the best LED light available on the European (possibly global) market right now. There are two notable companies that use these in their grow lights at the moment: Budmaster and Plant Photonics. We highly recommend either of these brands as their products have been thoroughly tested by the community and their customer service is great. While prices are high, established brands like these make superior products and are always willing to help you get started.
There are also many cheap, nameless options for growers that are on a budget. These cheap LED grow lights are currently flooding the market and are a solid choice for growers that simply want to get started for as little money as possible. If you decide to go the cheap route, try to find an LED grow light that uses 3W diodes, as these are generally superior to 5W, 10W or even double chip models. We know that these lights can produce excellent results, but they do often have issues with heat, sound and warranty.
Picking a new grow light can be complicated, but whichever lights you pick you’ll want to think about how much light is reflected off of the wall. While this may not be a big issue with very focused LED grow lights that only spread their light at a 70 degree angle, growing cannabis under HID lights needs all the reflection it can get. In some setups adding reflective material to the walls can increase yields by almost 30%! Grow tent growers usually don’t have to worry about this as the entire inside of most grow tents is made of high quality reflective material.
For those of us that do not grow in tents there are a few different options for wall reflection, these largely depend on the investment you’re willing to make. In general light should be diffused by the reflective material to avoid burning your plants. This is also one of the reasons why using mirrors is a bad idea.
You can chose between using paint, foil or rigid sheets. There are great products in all three categories, but using foil does require some special attention. If not installed carefully, air pockets or other irregularities can cause hot spots.
While aluminum foil or heat blankets might seem like a good idea, there are much better options in the same price range. Many growers use simple panda foil to cover the walls of their grow space when starting out. This type of foil gets its name from being black on one side and white on the other. The white side of panda foil reflects 80-90% of the light that hits it, which is great if you consider the fact that the price is negligible. White latex paint is another great low budget option and is similar to panda film in terms of reflection (80-90%).
Higher end, more expensive products include mylar foils or sheeting which reflect 90-95% of light. Thicker mylar sheeting also has the advantage of blocking out infrared light, making your grow less detectable through IR-cameras. We definitely recommend thick mylar if you can afford it, as thinner mylar can be difficult to clean.
After helping you decide which type of grow light you want to use, we hope to have helped you decide on which specific light to buy and how to use it as well. Especially for LED growers this can be extremely difficult, which is why we’ll address this issue in a follow-up article about LED grow lights. We At Spliff Seeds wish you and your garden the best of luck with your new grow light!