Grow room utilities / 01
Know what your lights will cost.
Then see what a different setup could change.
Compare fixture draw and daily run time on the same electricity rate. Get lighting energy, cost and the heat equivalent—with the math in view.
The comparison desk
Start with your current setup in A. Change B to test another fixture or run time. Both use the billing terms below.
Shared billing terms
Use your own rate.
$0.16/kWh is an editable example.
Baseline
Use actual electrical input watts at the dimmer setting you plan to run.
Alternative
A lower cost alone does not establish equal light output, coverage or yield.
Alternative estimate
Annualized = this daily schedule for 365 days.
B compared with A
Change B to see the difference.
—per billing period—
Power × time
Bars show daily on-time, starting at zero for comparison. They are not timer start times or a recommended photoperiod.
—
Save inputs, estimates and assumptions together.
Follow the energy
Power tells you the draw while the lights are on. Energy adds the time. Your rate turns that energy into cost.
Divide by 1,000 to get kilowatts.
650 W × 8 ÷ 1,000 = 5.2 kWDaily consumption in kilowatt-hours.
5.2 kW × 12 h = 62.4 kWhThe lighting energy charge for your period.
62.4 × 30 × $0.16 = $299.52Lighting at a constant electrical draw and a single rate. Use measured draw or the manufacturer’s input-power specification—not an “equivalent wattage” in a product name.
At the example settings, eight 650 W fixtures use 1,872 kWh and cost $299.52 over 30 days. These are sample inputs, not a local tariff or a fixture recommendation.
HVAC, ventilation, pumps and dehumidification; demand charges, time-of-use pricing, fixed fees, taxes and tiered rates. Check your utility’s tariff before treating this as a bill forecast.
Lighting heat equivalent = connected watts × 3.412 BTU/h while on. This is an electrical-power conversion, not a complete cooling design or an air-conditioner energy estimate.
Explore all calculators →Method references: EIA · power and energy / U.S. DOE · utility rate components / NIST · unit conversions
No. The result isolates lighting energy. Use the HVAC load calculator to estimate cooling capacity, then model HVAC energy separately if you know the equipment efficiency.
Measured draw is best. If you do not have it, use the manufacturer input-power specification.
Nearly all electrical power used by lighting ends up as heat in the space, so connected watts are useful for cooling-load planning.
These are optional tools that fit the process described above. Choose by the job and the specs that matter—not by a product badge or a star count.
Primary indoor lighting
What matters: Match real canopy area and manufacturer flowering coverage; avoid wattage-name marketing claims.
Check current options on Amazon (paid link)Raise/lower fixtures as canopy develops
What matters: Load rating and adjustment range matter more than branding.
Check current options on Amazon (paid link)Automate photoperiod
What matters: Choose a timer rated for the actual electrical load.
Check current options on Amazon (paid link)Light/environment containment
What matters: Size from canopy and equipment footprint, not plant-count marketing.
Check current options on Amazon (paid link)(paid links) As an Amazon Associate I earn from qualifying purchases.
Lighting is one part of the room. Check cooling, moisture and space before choosing the rest of your equipment.
Choosing fixtures? Compare grow light types and LED grow lights, then plan your schedule with room controls and timers.
