Along with water,  hydroponics plant nutrients, Co2 and oxygen, grow light is the key basic component, required by plants to live. Providing additional light is necessary for indoor gardening. Furthermore, light should resemble the sunlight as much as possible. In order to achieve that goal several types of lights are used: incandescent, fluorescent, high intensity discharge or HID lamps and sulfur lights. While there are many other types of lighting, only the mentioned above are recommended for indoor gardening. The major concern with other types of lights is that they do not produce light in the appropriate spectrum, required by plants.

Though typical widely used incandescent lamps fit any ordinary light socket, this type of lighting is considered to be the least effective in lighting your garden in comparison with other types of lighting. Incandescent lights produce light in the red spectrum; that is why such lamps are commonly covered with a blue coating in order to increase the amount of blue spectrum in the produced light. In general, incandescent lights are considered to be poor options for indoor gardening needs.

In comparison with incandescent lamps, fluorescent lights produce more light with lower energy consumption. However, the light, produced by fluorescent lamps, is not intensive enough and cannot penetrate more than 6” – 8”. Light, produced by fluorescent lamps, is usually simply insufficient to provide normal growing of plants, vegetables and flowers. The only application, where it is possible to use fluorescent light, is growing seedlings, cuttings, or some particular plants with low light requirements, such as orchids.

High intensity discharge lights, also known as HID lights, are currently the most effective lights for indoor gardening. Metal halide (MH) and high pressure sodium (HPS) lamps are two major types of HID lights. Each type produces light in a particular range: for example, metal halide lights generate blue spectrum light similar to the full summer sun, and high pressure sodium lights produce light in red and yellow spectrum, resembling the autumn sunlight. 

Though high pressure sodium lamps usually are more expensive (by about 10%-20%) than metal halide lamps, they are more durable with extended lifecycle. Besides, HPS lights feature higher lumen output (97-150 lumens per watt consumed) and lose only about 5% of their brightness after one year of use (for comparison, MH bulbs produce about 70-115 lumens per watt and  lose up to 15-20% of their initial brightness within a year). 

Irrespectively to the particular type of lighting in use, it is recommended to replace lights on the timely manner: MH bulbs – after 12-18 months, and HPS bulbs – after 24 months of work. Basically, metal halide lamps is the more preferred type of lighting for plants, when they grow, and high pressure sodium lamps suit best for flowering plants. However, the discussion on which type of lighting is best is still open among gardeners. Each type of lights offers its own advantages, as well as disadvantages, so it is often a matter of personal choice, preferences, growing environment and needs. The scope of this article is to provide plain information on the available types of lighting for indoor hydroponic gardening, while leaving readers enough space for personal decisions on which product to prefer.  By the way, recently a new type of lights appeared. The so-called conversion systems allow switching between MH and HPS lights when it is necessary simply by changing the bulb. Though this type of lighting offers certain benefits, conversion systems are still pretty expensive. More information on particular types of HID lights used in hydroponics systems will be provided in the next set of hydroponics guides.