Maximizing Supplemental Lighting  November 13, 2007 - 15:43  In
the northern half of the United States and in Canada, the total
quantity of light received per day, the daily light integral
(DLI), can be a limiting factor in the production of many
greenhouse crops from October until March. A common target
minimum average DLI is 10-12 moles per day (mol∙m-2∙d-1). There
can be several negative effects on crop quality when the DLI is
lower than the target minimum. For example, cuttings may be
slower to root; rooting of seedling plugs can be delayed; and
stock plants can have fewer branches and thinner stems.
Boosting the DLI, Not the Costs  To increase the average DLI
provided to plants, growers can only do a few things. First, the
number of overhead obstructions should be minimized. For
example, hanging baskets intercept light, so the DLI is reduced
on crops below. Second, the glazing can be cleaned so there is
no leftover whitewash or dust or grime that accumulates on the
glazing material. Third, a grower can