March 2023 - 13

PRODUCTION
the DesignLights Consortium at www.
designlights.org/horticulture. Note that
there are large differences among the
many fixtures listed, but the webpage
has nice functionality to help you sort
based on characteristics you consider
important, such as power, light output,
efficacy and many others.
Upgrading your lighting system to LEDs
is not always the best option. If your
electricity is relatively cheap and you
don't use the lights very much, look into
maintenance first. HPS fixtures should
be replaced after 4,000 to 5,000 hours
of use, but in many cases, growers try to
get more life out of their aging bulbs.
HPS fixtures inevitably become less
efficient over time. Because this decline
in light output happens gradually, it can
be hard to notice. The only way to be
sure how much light your fixtures provide is to measure
it with a PAR (photosynthetically active radiation) sensor.
Take readings every few months when there is no sunlight
and the lighting system is on at full power. Do so at
multiple locations in the greenhouse. Then plot the light
levels over time to monitor how quickly the light levels
decrease. In many cases, simply replacing the HPS bulbs,
rather than replacing the entire lighting system, is still the
most cost-effective option.
And when you replace HPS bulbs, clean the reflectors at
the same time. Just like the bulbs themselves, reflectors
can become less efficient over time. Some of this is
due to aging and irreversibility. But in many cases, dust
accumulation can reduce the performance of reflectors.
A quick cleaning of the reflector can increase the light
output of a fixture - a simple, quick task that is all too
often overlooked.
CONTROLLING YOUR LIGHTS
Installing and operating supplemental lighting is
expensive, so it is important to get the most possible
value out of it, and that requires a good way to control
the light fixtures. LED fixtures provide major advantages
over HPS fixtures when it comes to control. The vast
majority of LED fixtures on the market are dimmable, and
the lights respond instantaneously to a signal that is sent
to the fixtures. HPS fixtures, on the other hand, require a
warm-up and cool-down period and cannot be dimmed
precisely. A common question related to dimming LED
fixtures is whether it affects the longevity of the fixtures.
And it does not. Dimming LED fixtures reduces their
operating temperature, which can slightly increase their
A lighting control
system used to
control supplemental
LED lighting in a
cannabis greenhouse.
efficiency (but typically not enough to worry about). A
lower operating temperature can also extend the lifespan
of the fixtures.
It is important to remember that LED fixtures are not
just simple, more efficient replacements for HPS fixtures;
LED fixtures offer control opportunities that go far beyond
what can be done with HPS fixtures. When switching
from HPS to LEDs, it is important to evaluate whether the
current control system is still the best option. Or is it time
to upgrade your lighting control system as well? Let's look
at the most popular lighting control approaches.
Timers are simple, cheap and crude. While using
timers to turn the lights on and off is the simplest and
cheapest approach, it cannot give you good control over
your growing environment. By their very nature, timers
cannot respond to changing weather conditions, unless
someone is regularly checking the weather forecast
and reprogramming the timers accordingly - not a
very practical approach and, in practice, the timers get
reprogrammed only a few times a year. Given the costs
associated with installing and operating a lighting system,
more advanced lighting control approaches will provide
better value.
Threshold control is a step up. In many cases, the
supplemental lighting is controlled based on how much
sunlight there is. Whenever the sunlight drops below
a particular threshold, the lights are turned on. This is
typically combined with a timer to ensure that the lights
don't run 24/7. With HPS fixtures, threshold control needs
to account for the required warm-up and cool-down of the
fixtures, so it is typical to leave the lights on for at least half
an hour, and once they are turned off, to leave them off for
at least 30 minutes. With LED fixtures, this is not needed,
GREENHOUSE PRODUCT NEWS 13
http://www.designlights.org/horticulture
March 2023

Table of Contents for the Digital Edition of March 2023
