Choosing the type of lighting to suit your needs is an important decision to make before you start growing indoor marijuana. High Intensity Discharge grow lights (HID) remain a popular choice, whether it be HPS or MH particularly for novice growers due to their low set up cost. If you are interested in LED grow lights we discuss that here.
What are HID grow lights?
High Intensity Discharge (HID) grow lights provide a cost-efficient light source for the growing and cultivation of hydroponic marijuana. HID grow lights are considerably cheaper than LED lights, and whilst less effective overall, still represent a tried and tested option for many growers. Two types of HID grow lights can be used for indoor marijuana growing – High Pressure Sodium (HPS) and Metal Halide (MH).
Either type can be used for a full grow from seed to harvest but it is not recommended, or the lights can be alternated at different stages of plant maturation, taking advantage of the strengths of each type of light to maximize the plants’ growth and yield. Starting with MH during vegetative and then moving to HPS during the flowering stage.
HID grow lights – Common sizes in Watts
1000 Watt – Hang 18 to 26 inches above the canopy
600 Watt – Hang 12 to 18 inches above the canopy
400 Watt- Hang 9 to 12 inches above the canopy
250 Watt – Hang 6 to 8 inches above the canopy
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The choice of Watt size will be determined by the number of plants you want to grow, the grow area, the strain of marijuana being grown and the amount of vegetative growth required.
Bulbs below 400W are usually seen as inefficient in our opinion and you are probably better off getting a CFL grow light.
Bulbs at 1000 Watts and above are also considered inefficient for most indoor growers. 1000W bulbs are big, they produce a lot of heat, need space over the top of the plants, work better with C02 and generally are terrific if you are more of a commercial grower.
Most hobby growers will do very nicely with 400W and 600W models.
You can buy multiple 400W and 600W models, space them out, reduce hot spots and get a more even grow area when compared to just buying one big 1000W model.
One 1000W or a 400W + a 600W will do well for 10 to 15 plants or five big ass plants using 3 to 5 gallon pots. Work back from there for the smaller Wattage lighting setups. Try and think in lumens as a standard, 10,000 to 15,000 per sq ft with most successful growers in that range.
Take a look at the table below and you will get a good idea of how many Watts you may require to achieve your growing goals.
You will note from the table above that lumens drops off considerably as you move away from the light. The calculation is Intensity = Light output / divided by distance squared. Less light but spread over a larger area.
Twice the distance will be ¼ of the lumens, for example a 1000W might offer 400,000 lumen at 4 inches but only 100,000 at 8 inches;
Three times the distance will offer 1/9 of the lumens;
Four times the distance will offer 1/16 of the lumens.
Metal Halide (MH) grow lights
The majority of Metal Halide (MH) grow lights produce light in the blue spectrum 6,500 to 7,200K which replicates natural light during spring and autumn. As a result, MH grow lights are best to use during the early vegetative stage of marijuana production.
When used as a primary light source in an indoor setting with no natural light, MH lights will encourage excellent leafy green plant growth, stems, branches and leaves which will produce shorter more bushy sized plants.
MH lights can be used throughout the entire grow cycle but this is not advised. The best method is to start with MH for the vegetative stage and then move to the HPS for the flowering stage, however if you only have the chance of buying one bulb always buy the HPS bulb as it will do better for an entire grow than MH.
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Whilst HPS grow lights are very efficient their lack of light in the blue spectrum makes them okay for the vegetative stage of indoor growing where no natural light source is available but not ideal. Indoor plants grown only with HPS light during the vegetative stage will generally be too skinny and grow too quickly.
Where HPS grow lights come into their own is during the flowering or reproductive phase of marijuana growth. The light from the orange/red spectrum is perfect for triggering hormones in the plants which increases budding/flowering of the marijuana. Marijuana grown hydroponically using HPS grow lights will generate a better yield than that grown using only MH lights.
On the downside, HPS lights use a lot of energy and create a lot of heat, which needs to be dissipated with air-conditioning or an exhaust system which requires more upfront investment from the grower.
Combining HPS + MH grow lights
More sophisticated growers often combine both MH and HPS grow lights, using MH grow lights as the primary light source with HPS grow lights only introduced to the lighting system as a secondary light source during the flowering stage.
Alternatively, it is possible to purchase combined MH and HPS grow lights in the same reflector, either with integrated or separated ballast assemblies. This solution is not considered particularly effective as these lights are less powerful, more expensive to purchase and have a reduced lifespan.
A better solution is a light fixture which provides the choice of using either MH or HPS lighting, but not concurrently. Such lights are known as two-way, switchable or convertible lights. Using these lights, it’s easy to switch from MH bulbs to HPS bulbs at the reproduction stage.
High Pressure Sodium vs Metal Halide grow lights
AdvantagesCost efficient, simple and easy to use, particularly for small cropsLong lasting, produce higher yields, better as secondary light source, good for use in cool areas
Metal Halide lights
High Pressure Sodium lights
Orange to red
Up to 10,000 hours
Up to 18,000 hours
Best for stage of plant growth
Reproduction / Flowering
Cost efficient,simple and easy to use,particularly for small crops
Long lasting,produce higher yields,better as secondary light source,good for use in cool areas
Not as long lasting as HPS lights, lower yield if not used with HPS lights
Use a lot of energy, produce a lot of heat, not suitable for confined spaces
Yields from HID grow lights
The expected yield from any given grow light is highly affected by the type of marijuana strain you buy, the quality of the light (new or old), environmental factors such as heat, humidity and airflow, the hydroponic setup and of course their food / nutrients you use. We have given an outline of what you might expect; the Holy Grail so to speak is 1 gram per Watt but not even some of the pros get that.
HPS light – yield*
MH light – yield
80 – 250 grams
Approx 10% less than HPS**
120 – 400 grams
Approx 10% less than HPS**
250 – 600 grams
Approx 10% less than HPS**
350 – 1000 grams
Approx 10% less than HPS**
*The actual yield of marijuana bud produced varies considerably based on many factors, mainly the competency of the grower!
**Whilst producing less bud than HPS lights, MH lights contain some UVB light which can increase the strength of the marijuana produced.
HID grow light system cost comparison
HID grow lights are much cheaper to purchase than LED lights, but the low up-front cost is offset by their reduced lifespan, higher use of electricity, excess heat generation and limited light spectrum. LED grow lights are cheaper in the long run.
Always be sure to purchase your lights and lighting system from a reputable source. You want to be confident that the product will work as advertised and that customer service is available should there be an issue.
*The system examples in the comparison above include ballast, reflector and lamp and are suitable for either Metal Halide or HPS lights. Systems with digital ballasts are priced at the higher end of the range.
Your grow light is not cheap to run. Plants need a huge amount of light and when you take them out of the free sun to your inside bunker you have to replicate that solar ray they want. The more light they get the more juice (nutes) they will inhale and the bigger and badder they will get.
Here is the average cost of electricity based on kilowatt per hour (kWh)in the USA. US Energy Information. Scanning down the list when this article was written Washington it only costs 8.93 cents per kWh and the highest was 36.79 cents in Hawaii – quite the difference, but then against those Hawaiians have it good and just grow outside anyways! An average of around 12 cents per kWh is a fair residential yard stick for the USA.
6 weeks on average for the vegging at 24 hours a day = 1,008 hours;
6 weeks on average for the flowering at 12 hours per day = 504 hours;
Total = 1,512 hours @ 12 cents = $181 USD in electricity.
Popular HID grow light brands we recommend
HID grow lighting systems
A lighting system for growing hydroponic marijuana using HID grow lights comprises the light bulb(s), a reflector (or hood) to maximize the efficiency of the bulbs and a ballast which powers the bulbs.
As well as different sizes and types of light bulbs, there are also different technologies available for both ballasts and reflectors.
Ballasts are available in either magnetic or digital types. Magnetic ballasts are a conventional method of regulating power to the bulb via a system of coils and condensers. Digital ballasts are more sophisticated, providing a constant energy stream which boosts the output of the bulbs and also provide settings for greater control of the light output. Ballasts are available which will run either type of HID grow light – MH or HPS.
We always recommend you buy a lighting set including the reflector, bulb, and ballast. The guys behind iPower have some fantastic gear.
The reflector, or hood, is another important part of the lighting system when using HID grow lights as it helps to maximize the efficiency of the light produced. Several types of reflector are available including wing, parabolic, air (or non-air) cooled and water cooled.
If you are starting out, it is recommended to purchase a whole system rather than trying to buy each component separately. Luckily, there are lots of retailers (both online and traditional) who will happily sell you a full HID lighting system which suits your needs.