If you’ve ever built or updated a growing operation, you know that lighting is a tough decision. Even when you dive into catalog, PAR graphs, and phone calls with salesmen, answers can be elusive. To make things worse, you have a looming cloud of pressure reminding you that if you choose the wrong lights, you run the risk of installing your lighting late and slamming your farm with unexpected lighting costs.
If that’s you, don’t worry. A basic understanding of lighting types will decode most of those catalog and tables.
Even if you already have lights, switching light equipment can sometimes still save you money. Different light types like high intensity discharge (HID), light-emitting diodes (LED), fluorescent, and plasma lights all create different dynamics in the farm.
This guide to lighting will explore the main types of grow lights, how they function, the quality of light they provide, and the costs that they represent (both obvious and not-so-obvious). By the end, you should know which type of lighting is best for you.
High Intensity Discharge
These lamps emit light when electricity is arced between electrodes inside a tube. After being turned on, the arc heats and evaporates gas and metal salts inside the tube. When this happens, it results in ions and free electrons, the parts that make up plasma. The plasma intensifies the light being emitted from the arc, and the HID lamp is running at full power.
Two common types of HID lighting are high pressure sodium (HPS) and metal halide (MH). The difference between the two is in the dominant wavelengths emitted. Metal halide lights typically produce more blue light (cooler) and HPS lights produce more red and orange light (warmer). A choice between the two often comes down to the growth stage and flavors a grower is trying to achieve, though HPS is the most popular.
Traditionally, serious indoor growers have relied on HID lighting to provide or supplement light to their crops. Such lighting provides high-intensity light with a good spectrum for plants, but with the price of high heat output—which results in high operating costs—and, ultimately, low light production efficiency.
Once the leading lighting type for greenhouse and indoor growers, HID lamps bring several implications with their design. Maintenance can be tricky, since the special glass tube used to house the electrodes and plasma can’t be touched with oil. This includes the oil on your hands, so you need to wear gloves when replacing bulbs. High intensity discharge bulbs also have shorter lifespans; most emit for a few thousand hours before needing replacement.
Despite some disadvantages, many growers still choose HID for financial reasons. It has a much lower up-front cost, so if you’re starting a small grow then scaling up, HID could be a great first option.
Like HID lamps, fluorescent lights emit light when an electric current passes through a bulb containing a gaseous substance. In this case, the gas is mercury vapor, which emits ultraviolet light when ionized. When passed through a phosphor coating on the bulb, this short wave ultraviolet light can be converted into longer-wave light—that is, visible light.
Another similarity between HID and fluorescent is that they produce more heat than LEDs as a function of their design. Unfortunately, this is unlikely to change; fluorescents and HID lights have neared their limit for efficiency, while LEDs are still a young technology with room to grow.
Energy use of fluorescents is generally lower than that of HID, though growers should be careful to choose high-output (marked with an HO on the bulb) fluorescents—T5s are typically HO. Avoid low-output lights such as T12s if possible.
Fluorescent lights have been used for a long time in indoor operations, but lack the intensity for serious production. Capital expense and operating costs of fluorescents are fairly low compared to HID lights. Replacement and disposal costs, along with fragility and a non-specific spectrum, have limited the use of fluorescents in larger indoor operations.
Light-emitting diodes are a type of lighting that use semiconductors. A LED is a device that emits light as one specific wavelength when energy passes through it. Two types of materials, each a different kind of semiconductor, are joined to create the diode. As energy passes through the device from one semiconductor to the other, a mismatch charges results in an excess of energy. This excess energy is emitted as light.
Several advantages have made LEDs the top lighting choice for modern indoor and greenhouse growers. Diodes can be sorted and chosen per light, allowing growers to hone in on one specific spectrum for their crops. Lack of a filament and moving parts and a longer lifespan mean less troubleshooting and fewer replacements. Finally, LEDs typically produce 30-50 per cent less heat than other lights. This benefit is incredibly important to energy costs, heat removal, and light lifespan.
Because the semiconductor industry has grown so much in the last three years, and since the demand for high-efficiency grow lights has been so important, the LED industry had the perfect opportunity to grow. As a result, the cost of LEDs has come down significantly.
Although LEDs are becoming more accessible, the greatest obstacle between growers and LEDs is cost. For growers trying to make a short-term return on investment on a small farm investment before expanding, LEDs might not be the best option. For long-game growers, however, LEDs are usually the best choice.
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Light-emitting diode lights belong to a rapidly growing industry with continually decreasing costs. Benefits such as ruggedness (LEDs are solid state), efficiency, dropping cost of manufacturing, low operating costs, and spectrum specificity tip the scales in favor of LEDs for indoor growers, even despite higher upfront costs.
Plasma lighting has been hailed as the high-efficiency sister to LEDs. The main differences between the two are that plasma has a shorter lifespan, less versatility and customization in terms of spectrum, and higher light output in lumens.
Induction lighting, similar in ways to fluorescent, uses magnetic fields rather than filaments to produce light. Induction lights have long lifespans and moderate efficiency. Induction lights have not found significant traction in the farming industry.
While the field of agricultural lighting is expanding day by day, the two main options used by growers are HID and LED lights. The primary factor that helps growers choose between the two is start-up speed. Growers starting with very limited budgets tend to start with HID; those with the money to invest in LEDs do so.
For more information, check out the rest of the lighting articles by Maximum Yield.