Expecting a value between 5 and 45, when in doubt go high.
moles per square meter per day of PAR.
How many hours per day will you run your lights?
Expecting a value between 12 and 20.
hours.
There are 57600 seconds in 16 hours. To get 12 mol per day per square meter of PAR in this time you need a PPFD of 208 umol per second per square meter of PAR.
How big is your grow area?
For rectangular grow areas. Expecting a value between 1 and 1000.
square ft or
square meters.
With an area of 2.00 square meters you will need a total PPF of 416 umol per second across the grow area.
What is the PPE of your lights in umol per Joule?
If you cannot find this info for the lights you are looking at then look at different lights. All good manufacturers should provide it. These values are just for rough guidance.
Light Type
umol/Joule
Flourescent
0.9-1.2
High Pressure Sodium (HPS)
0.9-1.8
LED
0.9-2.7
Ceramic Metal Halide
1.2-1.5
Household LED bulbs
1.5
Theoretical Optimal LED
4.6-5.1
Expecting a value between 1 and 2.5.
umol per Joule.
To get a PPF of 416 umol per second across the grow area with 2 umol per Joule you will need lights with at least 208 watts of power. This is actual electricty drawn from the wall.
What is your cost of electricity in $ per kwh?
Expecting a value between $0.01 and $0.5 per kwh.
$
With a cost of $0.12 per kwh and using 0.21 kwh you will spend $0.40 per day and $12.00 per 30 day month.
Final result.
Get lights which use 208 watts of actual electricity or more. This will use approx $12.00 of electricty per 30 day month.
What is DLI? Daily Light Integral is the amount of light, which the plant
can use (PAR), which hits a one sqaure meter area in a day. It is measured in moles per square meter. For example a grow setup might have a DLI of 12 moles per square meter per day of PAR. It is hard to give a solid number for any plant because at different light levels the plant will grow at different speeds. Therefore if you want to get a better understanding it's important to do your own research.
What is a mole? One mole (mol) of something is 6x10^23 of it, which is a very big
number. So one mole of photons is 6x10^23 of them. This number is also known as Avogardo's Constant
It is also important to know about umol which are micro moles which are one millionth of a mole.
What is PAR? Photosynthetically Active Radiation is light which a plant can use
to power photosynthesis. This means that it will be in the 400nm-700nm range.
What is PPF? Photosynthetic Photon Flux is how many photons which are useful to a plant (PAR) which are produced by a light per second of operation. It has units of umol per second.
What is PPE? Photosynthetic Photon Efficiency is how many photons which are useful to a plant (PAR) are produced by a light from one Joule of electricity. It has units of umol per Joule.
What is PPFD? Photosynthetic Photon Flux Density is how many photons which are useful to a plant (PAR) which are hitting a one square meter area in one second. It has units of umol per second per square meter.
What are Joules and Watts? Joules are the unit of electrical energy, basically how many electrons is your appliance using. Watts is a measure of Joules used per second.
My lights say they draw 30 Watts of electricity but are equivalent to a 300 Watt light, is this an amazing deal? No. There is no free lunch in plant lighting. This calculator works out the actual amount of power you need to pull from the wall.
More Info There is a comprehensive lighting guide here if you want more information.
You can donate if this calculator helped you :)