This is a mechanism in plants that tracks time. Plants respond to the length of light and darkness that they receive. It is actually the length of darkness that initiates the response by the plant. Different plants respond differently.

Long-Day Plants — are those that require a minimal dark period in order to flower. Long-day plants generally require a minimum of 16 hours of light to trigger flowering. The rule of thumb for lighting of long-day plants is to increase lights from approximately 14 up to 16-18 hours per day over the normal lifecycle of the plant.

Short-Day Plants — are those that require at least 12 hours of darkness to flower. Plants in this category usually require 16-18 hours of light for the vegetative cycle and approximately 12 hours of light to initiate bloom cycle.

Day-Neutral Plants — do not respond to the length of light or dark periods. These plants may respond to temperature or days to maturity instead. Most vegetables are day neutral. Generally plants in this category can be grown with 12-16 hours of light.

To determine foot-candle levels, we recommend using a Light Meter.