system for the same area would be calculated
as follows. Four MH fixtures at 450W each × 4
(racks) = 16 fixtures using 7200W. The cost of
$185 per fixture × 16 fixtures = $2960 total for
the equipment. Take the total of $2960/240 ft2
= $12.33 per ft2 for the comparable MH grow
light equipment. Finally, the electricity consumption can be determined as 30W/ft2 (by
calculating 7200W/240 ft2).
The LEDs are more expensive upfront
but more efficient with 30% lower ongoing
operating costs. Now, we want to answer the
question “How much savings comes with the
more efficient lights?”
We need to set two key variables that you
can adjust accordingly. For the purpose of
this calculation, we will use daily hours of
illumination — 16 hr (5840 hr/year), and
cost/k Wh — $0.12 (US average).
Key square footage data points are:
• Ongoing energy (30W for LED - 20.8W for
MH) = 9.2W saved/ft2
• The upfront cost difference ($33.33 LED
- $12.33 MH) = $11 saved/ft2
The related formulas are:
• Watts saved/1000 × Annual hours =
Annual k Wh savings/ft2
• Annual k Wh saved × Cost/k Wh = Annual
• Added upfront cost/Added annual cost
savings gives the payback time
So, for example, the calculations would
• 9.2W saved /1000 × 5840 hr = 53.7 Annual
k Wh savings/ft2
• 53.7 Annual kWh saved × $0.12 = $6.44
Annual cost savings/ft2
•$11 Added upfront cost/$6.44 Added
annual cost savings = Payback time is
1. 7 years
Over the long 100,000-hour life of many
LEDs, the payback in just over a year and a
half presents a favorable business advantage.
For a facility with 24,000 ft2 of grow area, the
annual savings of $6.44 adds up to $154,000
per year and more than $1.5 million over 10
years. An increasing number of LED manu-
facturers and value added resellers (VARs)
offer $0 upfront cost financing options. So in
your review of product options, make sure to
ask about flex payment and financing plans;
then the monthly energy savings can pick up
the cost of the LEDs rather than your work-
ing capital upfront.
Step 3: Order samples of the two or three
horticultural lighting solutions that are mathematical winners with the lowest equipment
cost/ft2 and the lowest W/ft2. Ask the manufacturer to refund the cost of the samples
if you return the technology within 90 days.
Step 4: Request refinements to the wavelengths if necessary and review monthly
financing options for all or partial payment
of the equipment.
Step 5: Place a purchase order with the com-
pany that delivers on the mathematical prom-
ise and on the in-field performance to meet the
needs of your plants and your business.
As we have explored, not all LED horticultural lighting is created equal. Let’s recap the
main points when selecting LED grow lights.
Ask manufacturers for photometric layouts
to see the PPFD at target elevation levels, and
look for the most even PPFD distribution over
hot spots. Line up fixture comparisons based
on apples to apples solutions that cover the
same area at the same wavelength and PPFD
levels. You can even out the fixture variables by breaking the performance down to
the square foot. Use the equipment cost per
square foot and the electricity operating cost
per square foot to guide your decisions. Test
samples before making a large purchase, and
ask the manufacturer in advance to agree to
refund the cost of samples that you don’t
keep. Last, financing will allow the monthly
savings to help pay for the lights and maximize your return on investment.
Sample calculation worksheet for pricing by area and specs.
Sample specification Notes
Grow plane area (e.g., 10× 24 ft) =
240 sq ft
Different manufacturers will have a different number of
fixtures and configurations. The goal is to review price not
on fixtures but on average area.
Target average PPFD = 375, at
measurement distance to planting
bed of 24 in.
Some manufacturers may not be able to reach the average
PPFD at the target height, so you can choose to make
exceptions and take that into consideration with “hot
spots” versus an even PPFD.
Wavelength (e.g., 14-part mix) =
Blue ( 3): 450 nm
White ( 2): 6500K, 380–750 nm
Red ( 3): 625 nm
Deep red ( 5): 660 nm
Infrared ( 1): 730 nm
Pricing per solution based on above:
Have your lighting provider fill in these blanks on price and
wattage to let you compare apples to apples.
Wattage per solution based on
Pricing per unit typically comes down with volume orders,
so you may want to ask for pricing based on 100 solutions
— in this case coverage area of 24,000 ft2.