These maps are intended to give growers a better indication of the expected cumulative light levels in their respective regions.
For the greenhouse grower, these average cumulative light levels represent those OUTSIDE the greenhouse. It is safe to assume that approximately 50% of the light levels noted on these maps are the average expected light levels INSIDE the greenhouse.
In Seattle, WA during the month of January they receive 5-10 Moles/Day on average OUTSIDE THE GREENHOUSE.
In Seattle, WA during the month of January they receive 2.5-5 Moles/Day on average INSIDE THE GREENHOUSE.
This measurement of cumulative light levels, expressed in Moles/Day, represents the total amount of photosynthetic Active Radiation (PAR) received over the course of an entire day.
Most floriculture crops have an optimum cumulative light level (moles/Day), and can be found on pages 77-79 of the 17th ed. of Ball Redbook. Theses maps will enable growers to evaluate the differences between their existing light levels and those need for optimum plant response.
Determining Cumulative Light Levels Using HID Lighting
To determine the total accumulative light delivered from an HPS supplemental lighting regimen.
Amount of Light Received X .00047 X Hours of Operation = Cumulative Light Level (or Moles/Day)
Example: 400 Footcandles X .00047 X 12 = 2.3 Moles/Day
If a grower in Seattle implemented the above example, then during the month of January they would receive an additional 46%-92% in usable light energy for their crop.