A lighting footprint, or
light footprint, is the area that a particular light fixture is
capable of illuminating. The term is more frequently used in indoor gardening
situations where artificial lighting must be used.
The most common lighting footprint today is 4x4 feet. This is due to the use of conventional incandescent bulbs traditionally used in indoor growing applications. However, lighting technology has evolved considerably, and today, there are numerous other options, including LED lighting, T5 light bulbs, and more. Each of these options has a different lighting footprint.
In indoor gardening, whether we’re talking about a handful of plants grown in pots, a hydroponic system, or something else, artificial light is needed to ensure plant growth and health. Each light fixture used produces a specific amount of light; this is called a lighting footprint.
Understanding the lighting footprint of different bulb types and bulb arrangements is important for indoor growers for a number of reasons. One of the most important is that this will determine the number of plants (or the size of plants) that can be placed under the bulb or fixture. This will ultimately affect the number of plants that can be grown within that specific area (the number of light fixtures and their footprint sizes will affect the number of plants an area is capable of supporting in terms of square footage).
To increase or change a lighting footprint, indoor growers have several options. One is to use a light mover, which essentially moves a single light fixture back and forth over a wider area, allowing you to use just one light for multiple plants (and increasing the lighting footprint). Another is to use brighter lights, but in a configuration where fewer bulbs are utilized.
It's also important to make use of reflectors or hoods above the bulbs, which effectively casts the light downwards, ensuring the footprint is maximized across the plant canopy.