Product Manual

Turf-Tec International Daylight Indicator – Light Meter - Copyright 2013
Page 5 - www.turf-tec.com
Light Intensity
The light that drives
photosynthesis in plants is
Photosynthetically Active
Radiation, or PAR light. This is
also referred to as Quantum
light, because it is measured in
units of moles striking an area
over time. Though PAR light
ranges from 400 to 700nm, the
region brightest to human eyes
is the area of least effect on
plants.
Light meters measure light intensity – the instantaneous amount of light delivered to
an area. During the 24-hour light gathering period, the Daylight Indicator functions as a
light meter.
Cumulative Light (DLI)
If photons were raindrops, light meters would show the intensity of a rainstorm. A five-
minute rainstorm may look impressive, but often provides less water than an all-day
drizzle. As cumulative rainfall is measured with a rain gauge, the cumulative quantity of
light is measured using the Daylight Indictator, or a light sensor with a data logger. The
daily total of quantum light is called the Daily Light Integral, or DLI, and is measured in
units of molm
-2
d
-1
(commonly, moles/day). DLI quantifies the light available to plants
to perform photosynthesis. On a sunny winter day in the middle latitudes, a plant
receives about 9 moles/day. If it is cloudy, the DLI drops to 3 moles/day. In the summer,
the DLI for a sunny day is about 26 moles/day and 12 moles/day for a cloudy day. Each
type of plant has a different DLI range for optimal growth. DLI is directly correlated with
plant quality, and a minimum amount of light is required for healthy plants.