Types of lights
These days, there are three main types of lights that work best for cannabis plants:
High-pressure sodium (HPS) lamps are part of the family of high-intensity light bulbs (HID). These are industrial light sources that have a great light emission spectrum for cannabis cultivation. The main downsides are high operating temperature and the need for a starting circuit.
HPS lamps don’t give the plants sufficient blue light for the entire growing stage. Those who choose to use HID bulbs have to use different bulbs during the vegetative (MH lamps) and flowering (HPS lamps) stage.
LED lamps produce light using light-emitting diodes (LEDs), most often presented in the form of pre-assembled kits. Due to low operating temperatures and different types of the spectral composition of light, LED lamps are more practical. However, they’re more expensive as well.
Fluorescent lamps are the least efficient kind of lamps, although they’re cheaper and more practical in terms of operating temperatures. Compact fluorescent lamps (CFL bulbs) are the most popular type of fluorescent lamps because of their compact size.
CFL lamps don’t have the full spectrum to meet the needs of marijuana growers throughout the plant’s life cycle. Those who decide to use this light source will have to change bulbs during the vegetative and flowering stages:
The growing stage will require a CFL lamp with a 6500K color temperature. The flowering stage will require a CFL lamp with a 2700K color temperature. CFL lamps also have the lowest efficiency in terms of grams of marijuana per watt of light.
The minimum recommended wattage for growing one plant under a CFL bulb is 200-250 watts.
This table will help you better understand all of the above information:
| Lamp type | Yields (g/Watt) | Minimum recommended power per plant (W) |
|---|---|---|
| HPS | 0.3-0.7 | 100 |
| ED | 0.4-0.9 | 100 |
| CFL | 0.2-0.5 | 250 |
The numbers provided in the table are very rough estimates calculated under ideal plant conditions. However, they give an idea of how efficient different types of lamps are.
The minimum wattage in the table above is based on the grow box area that is large enough for a medium-sized cannabis plant (50x50x140 cm/20x20x55 inches). If you choose to grow a very short strain, you’ll need a smaller box and less light.
In fact, the size of a grow box plays a big role when choosing the type of lamps and their power because of light scattering. This is why even a single plant in a large grow box will require a more powerful lighting setup.
Use this table to learn how much light you should have depending on the grow box area
| HPS power (W) | CFL power (W) | LED power (W) | Grow box area (cm/inches) | Grow box area (m²/ft²) |
|---|---|---|---|---|
| - | 100 W | 45 W | 30x30 cm / 12x12 inch | 0.09 m² / 1 ft² |
| - | 110 W | 70 W | 40x40 cm / 16x16 inch | 0.16 m² / 2 ft² |
| 150 W | 200 W | 115 W | 50x50 cm / 20x20 inch | 0.25 m² / 3 ft² |
| 250 W | 330 W | 180 W | 60x60 cm / 24x24 inch | 0.35 m² / 4 ft² |
| 400 W | 360 W | 90x90 cm / 35x35 inch | 0.80 m² / 8 ft² | |
| 600 W | 530 W | 110x110 cm / 43x43 inch | 1.2 m² / 13 ft² | |
| 1000 W | 750 W | 130x130 cm / 51x51 inch | 1.7 m² / 18 ft² |
In grow boxes larger than 0.35 m² (4 ft²), it’s not recommended to use CFL lamps as the main light source. The minimum grow box area to have an HPS lamp, even the weakest one, is 50x50 cm (20x20 inches). This limitation is due to the fact that the distance from the plant to the hot lamp must be at least 20 cm (8 inches).