Light for the cannabis plants

An indoor cannabis set-up is likely to require at a minimum 2000 lumens per square feet. A lower volume of light is likely to limit the growth and slow the development of the harvest. A further aspect to installing the lights is the distance to the plants. Adjusting the lights on a day-to-day basis is likely to be a requirement in the early stages where the plants are rapidly growing. 

A light set-up of 2500 lumens per square foot is the likely target, although a rating of 3000 lumens is going to be beneficial if planning on enriching the CO2 levels. 

The ideal solution is likely to include the High Intensity Discharge Lamps (HID). A HID light is available in three options – Mercury Vapor, Metal Halide, and High Pressure Sodium. A metal halide lamp is able to offer an ideal level of intensity with improved spectrum. A high pressure sodium is quite similar to street lamps in that it is able to provide a light that appears yellowish in color, although orange or pink versions are also available. 

A high-quality HPS lamp is a versatile option and able to provide the ideal light source throughout the growth process. Studies indicate that a crop relying on the HPS lamps are able to mature seven to 10 days earlier than a similar setup with the metal halide lights. But you are likely to yield a better crop if you are able to wait the extra period. 

In the process of sourcing the HIDs you will likely find that the most cost-effective options are the mercury vapour and fluorescent lamps. A MV is able to produce 175 W per 8000 lumens, and the HPS is able to generate 150 W per 15,000 lumens, so you'll find that the HPS is certain to be the most desirable option. A MV light is able to provide the high-quality colour spectrum. A HPS is able to feature high in relation to the red colors, which is certain to benefit the flowering stage. And the MH is high in blue colors, which is more desirable in the vegetative stage. It is unfortunate that the metal halide lights provide the lowest quality in relation to spectrum for encouraging the growth of plants, but they are certain to be the most affordable option. In most cases these lights aren't recommended since they are quite expensive to run over the long-term. 

A HPS with 400 W is likely to output approx 45,000 lumens. For each 500 W of constant use the cost is likely to relate to £15 per month in electricity. So, if you're able to use a lamp that is able to provide a similar light source but with half the power you will notice that this is much more cost-effective and will provide significant savings in the future. By making the necessary operation costs vs. initial setup costs you are certain to create a more efficient and reliable set-up. A high-quality HPS lamp is certain to be able to cover its initial costs when compared to the slower and smaller sized fluorescent or MV lamps. 

Lamp W Lumens Efficiency Fluorescent 40 3000 400 W = 30,000 lumens Mercury Vapour (MV) 175 8000 400 W = 20,000 lumens Metal Halide (MH) 400 36000 400 W = 36,000 lumens High Pressure Sodium (HPS) 400 45000 400 W = 45,000 lumens 
From the chart above you can see that the MV lamps offer less efficiency then the fluorescent lights. A further point to consider is the Mercury vapour lights can't be located close to the plant top, so the plants aren't able to benefit from the MV light so readily. Also, light distribution isn't so desirable. A lamp of this type just isn't intended for an indoor garden set-up. Use the HPS, MH, or fluorescent lamps. A Halogen arc lamp is likely to produce excess heat and is not sufficient light, so these again aren't recommended even though they are able to provide the ideal spectrum for plant growth.
A modern style of HPS light is known as Son Agro, which is able to offer a watt range of 250, 400, and 1000. A 400 W light is closer to 430 W since a 30 W blue bulb is included. A light of this type is extremely bright with about 53,000 lumens which is sufficient for lighting a greenhouse and can be used in place of the HPS lamps. A quality aspect of these bulbs is that they are able to retain many qualities seen with the MH lights, like early maturation and minimal internode spacing, which are often lost with the HPS users.

The internode length for the plant life using the Son Agro lights are the most effective compared to most other types of lights. A harvest produced using this type of light is certain to produce the more bushy, fast growing, and compact plants. A negative of the Son Agro bulbs is that they aren't able to give the longer life cycle seen with the HPS bulbs. A lifespan is likely to be about 25% less. 

A further option includes the metal halide (MH) lamps that come with 400 W and 36,000 or 40,000 lumen bulbs. A higher rated likely is likely to be slightly more expensive, due to the extra lumens on offer. A MH light is likely to appear with a high degree of blue and more efficient than a standard HPS lamp in the stage of vegetative growth, although it does offer less efficiency then the HPS. A conversion bulb is available for the metal halide lamps which are able to adjust to something similar to the HPS lights, but you will likely find that a conversion is quite costly when compared to the colored Son Agro bulb. So, it might be more beneficial to rely on the straight Son Agro HPS lamp. Initial cost is likely to be more expensive but over the long-term you are certain to be more beneficial and are certainly more straightforward to hang then using multiple fluorescent tubes. 

If you install a set-up with a metal halide lamp with 36,000 lumen at 400 W and a HPS lamp at 53,000 with 430 W, which is likely to be the most energy efficient and provide the ideal yield. In most cases, you will find that the Son Agro HPS is the best option although it has come at a higher retail price. 

A set-up with the Son Agro lamps is certain to offer a better quality option compared to the MH for almost any situation. A MH is more cost-effective to purchase, but the lifespan is that much shorter. A HPS bulb is likely to last 21,000 hours compared to 10,000 hours for the MH bulb. A Son Argo is able to provide a lifetime performance of about 16,000 hours. A long life light with more energy is certain to be the more desirable option. 

A HID lamp is likely to benefit from horizontal mounting since this is able to increase the volume of light that is able to reach the plant life. A set-up of this type is likely to boost the light quality by 30%. Many of the HID are designed with the horizontal mounting fixtures for those intended indoor gardening use. 

A lamp set-up with the HPS is certain to be the most cost efficient to operate, but is often found to be available with 70 W bulbs in the DIY stores. Bulbs at this wattage isn't likely to be the most desirable option, but still more efficient than the fluorescent lights, so a small operation (9 ft.² of less) might benefit from these HPS lamps. A larger scale set-up that is above the 9 ft.² is certain to benefit with two or three lamps to provide the ideal light source. A two bulb set-up is able to provide approx 12,000 lumens from the 140 W, so a more preferable option compared to the fluorescent lights. But a single 150 W HPS is able to offer close to 18,000 lumens with a longer bulb life and more cost-effective to purchase. 

An issue is likely to relate to the mid-size lights with wattage at 150 or 250 which are often found to be just as costly to purchase as the large 400 W lamps. So, if you do actually have the space in the growth area it might benefit to initially invest in the 400 W bulbs. A professional set-up is likely to require the large-sized bulbs that may range in the region of 1080 W. Although a set up with two 400 W lamps is likely to offer improved light distribution. However, you'll likely find that purchasing two small lamps is more expensive than going for the single lamps, so you might want to consider which set up is most preferable for your operation. 

A build-up of heat is a noticed factor with the HID lights and the volume of light that is able to benefit plant growth is certain to relate to factors like PH, the nutrient availability, CO2 levels, and temperature. An oversized lamp for the room is likely to mean more aggressive venting, which is likely to impact the ability to enrich CO2 as this is being sucked out of the room.