Light is a very important thing when it comes to growing marijuana. You need the perfect amount, at the perfect place, at the perfect time in order to get perfect bud! When growing indoors, you shouldn’t go under 2,000 lumens per square foot. If you’re under this mark, plants will grow slowly, and the stem length will increase, allowing for less bud development. 3,000 lumens psf is optimal especially if you’re going to enrich the soil with co2, but a good goal is 2,500.
High Intensity Discharge lights are ideal for indoor growing. HID’s come in 3 basic types: HPS, or high pressure sodium, Metal Halide (MH), and Mercury Vapor. Metal Halide is basically a higher-intensity version of Mercury Vapor. HPS has a yellowish hue, which is sometimes pink or orange, similar to street lamps.
The nice thing about HPS lights is that they can be used from seedlings to budding stages. Many tests show that crops grown with HPS lights mature about a week later, but also produce more bud. The least expensive and easiest to find HID lights are fluorescents and mercury vapor. Mercury vapor lights put out about 8,000 lumens per 175 watts, while HPS puts out 15,000 per 150 watts. This proves that HPS lights are almost twice as efficient. However, the light spectrum from MV lights isn’t great. HPS is high in red lights, which has been proven to work well for the flowering stages. Metal halide has more blues, which are better for vegetative growth. MV lamps have the worst light spectrum for plants. MV lights are not recommended, even though they are cheap and easy to find.
You need to think about energy costs when deciding what kind of lights to use. A 400 watt HPS will output about 45,000 lumens. It costs about $20 per month in electricity costs for every 500 watts of continuous use. So, with some quick calculations you can see that, after the cost of electricity, the “cheap” MV lights will cost more than HPS in the long run. Plus, HPS lights always increase the yield, so they will pay for themselves after only a harvest or two.
Lamp type Watts Lumens per bulb Total Efficiency
Fluorescent 40 3000 400 watts = 30k lumens
Mercury vapor 175 8000 400 watts= 20k lumens
Metal halide 400 36000 400 watts= 36k lumens
High pressure sodium 400 45000 400 watts= 45k lumens
The above chart should help you make some decisions and calculate energy:output costs. You should take note that the MV lamps are much less efficient than the fluorescent lights. Plus, MV’s cannot be placed as close to the plants as fluorescents, so the plants will not receive as much light from them. Simply put, MV lamps are not suited for indoor grow ops. Halogen lamps are not recommended either, as they generate a lot of heat, while using a lot of wattage without much light output.A few years ago a new kind of HPS was released, called Son Agro. They are available in 250, 400, and 1000 watts. They are very, very bright (~53k lumens for the 400 watt) and intended for greenhouse growing. If you already own an HPS lamp, it’s a good idea to replace your existing HPS bulbs with these new ones, as they put out much more lumens with the same amount of watts. These bulbs are recommended because they are basically a hybrid between HPS and MH. These lights will help plants mature earlier, and unlike normal HPS lights, encourage minimal internode spacing, which allows for more bud to grow.
Plants grown under Son Agro lights are extremely bushy and will yield quite a bit. Internode spacing is also extremely good with these lights, with some of the shortest lengths ever seen. Plants also grow extremely fast, and will mature up to 2 weeks earlier than HPS lights. The only real downside to Son Agro bulbs is that they do not last as long as HPS. Generally speaking, HPS lights last about 25% longer.
Metal halide bulbs are another good option for indoor growing. They are available in both 36k and 40k lumens (both for 400 watts). The “super bulb”, which has 40k lumens, costs a bit more (usually $10-15 more). They last longer and put out more light, so if you can afford them they’re a good choice. MH bulbs are more blueish, and therefore better for vegetative growth. However, they are much less efficient than HPS bulbs. Personally, I recommend the Son Agro bulbs more than anything. Even though they are expensive, you will save energy costs in the long run, and they will help increase crop outs, helping you make more money.
Son Agro bulbs are better than MH in pretty much every way. The only thing MH really has going for it is affordability, but keep in mind that MH bulbs don’t last as long as Son Agro. 400 watt MH bulbs will run you about $36, while HPS costs about $40. Son Agro HPS are about $10-15 more. MH bulbs have a lifespan of ~10k hours, while HPS have an impressive 21k. Son Agro HPS lights last about 16k hours – less than normal HPS, but keep in mind that the output is higher, and plants mature quicker, meaning you don’t have to run the lights for as long.
The best way to use HID lights is to mount them horizontally on a ceiling, shelf, or by hanging them. This will boost the amount of light that hits the plants by about 30%. HPS lights are much cheaper than most other lamps, but it’s hard to find high-watt bulbs. The home improvement stores only carry HPS in 70 watts, which is a very inefficient. Of course, if you have a VERY small operation, you can get away with using 70 watt HPS in place of fluorescent lights. These 70 watt lamps cost about $40 each. If you have a less than 9 sq. ft growing area, you can use just 1 of these lamps. If you have more than that, at least 2 lights will be required. Of course, 70 watt bulbs are not recommended for larger grow ops, especially since you’d need to get 5+ of them to get enough light to your plants. If you have to buy 2 or more of these lamps, a 150 watt HPS is recommended, as it is more efficient and puts out more lumens. Plus, the bulbs last longer, and are cheaper. If you’re going professional, there is a 1080 watt HPS light available, but I think you’ll find that 2 or 3 400 watt lights work better, as the light will be more evenly distributed. However, 2 lamps will be more expensive than 1, so if you’re on a budget and just need a lot of wattage, a 1080 watt will do the trick.
With HID lamps, overheating can be an issue. You want your plants to be warm, but you don’t want to cook them. You don’t want to use too big of a lamp, especially if you don’t have a good ventilation system in place. Also, the amount of light that plants can actually use depends on several factors, such as: pH, nutrient availability, temp, CO2 levels, etc. If you have too big of a lamp, you’ll have to vent your grow room constantly, which means you cannot enrich CO2.
When choosing a bulb to use, keep in mind the costs. For HPS, a 70 watt costs $24, while 150 watt is $30, and 400 watt is $40. So, it’s always better to buy a larger watt, as it will cost you more to replace 2 70 watts than 1 400 watt. Plus, you pretty much cannot resell the 70 watts, while 400 watts are easy to sell on Craigslist. It’s recommended to spend all the money you can afford, so that you get the best setup possible. Especially since only $30 more will buy you about 20k lumens extra – enough to significantly increase the yield of your crop, and help plants grow big and strong. Below you’ll find a table of costs of various lamps/bulbs.
Type Complete cost Bulb cost Bulb life Lumen
HPS 400 $219 $40 18k hours 50k
MH 400 $175 $37 10k hours 36k
Son Agro 400 $235 $55 15k hours 53k
Super MH400 $190 $45 N/a 40k
MH 250 $149 $32 N/a 21k
HPS 250 $165 $36 N/a 27k
HPS agro250 $180 $53 N/a 30k
MH 150 $139 $25 N/a 14k
HPS 175 $150 $30 N/a 17k
If you want to buy these types of lamps, go to a local growing shop, or if you can’t find one, check the Yellow Pages. Look under nurseries, lighting, and gardening. There should be some indoor gardening stores in your area, and if you’re lucky, there may be a hydroponics shop nearby.