Definition - What does Lumen (lm) mean?
Lumen refers to the basic measurement of illumination emitted by a light bulb, tube or any other light source. In horticulture, it is important to grasp the basics of lighting to calculate the exact light exposure that plants and seedlings require to thrive.
Proper light exposure can prevent harmful pests and fungus from invading the roots and preventing proper growth.
MaximumYield explains Lumen (lm)
In nurseries and indoor gardens, fluorescent grow lights are often installed because of their low lumen values. Consequently, they are ideal for plants that do not require much light to thrive. Most grow lights with low lumen values are on the small side. They are also inexpensive, especially when compared to metal halide (MH) lights. These are white and blue in color and are often used to keep leafy plants compact. Metal halide lights can produce up to 125 lumens per watt.
Standard fluorescent bulbs, however, only produce around 40 lumens per watt, while incandescent lights produce a mere 18 lumens per watt. However, incandescent bulbs are not suited to large indoor gardens. For large and commercially oriented gardens, high pressure sodium (HPS) lights that can produce up to 140 lumens per watt are often recommended. These are more budget-friendly than metal halide lamps because of their long lifespan.