Lighting Calculation Formulas
To correctly determine the best lighting for your space there are several things you should know. At this point, some definitions are necessary:
Lumens – A lumen is the amount of light emitted by a candle that falls on 1 square foot (square foot) of a surface one foot (1 foot = 0.30m) away.
Watts – A measure of the amount of electricity flowing through the wire. Watts per hour measure the amount of watts consumed in an hour. One Kilowatt / hour (KWH) is 1000 watts / hour.
To determine the cost of operating your light:
Find out how much Kwh is charged on your electricity bill. Imagine you have a 1000 watt bulb and pay $ 0.5 / hour. If one kilowatts equals 1000 watts, you’ll pay 5 cents an hour to keep the light on. Another example. Say you have a 400 watt bulb and pay $ 0.3 / hour. Divide 400 by 1000 = 0.4 and multiply by 0.3 = $ 0.012 per hour of light.
To determine how many lumens per square foot:
You have to find the area of your space. (width X length = square foot) Divide the number of available lumens by the square foot measurement of your area.
Example: Let’s say you have a space of 3 feet deep by 4 feet wide = 12 square feet, and the total lumens of your lamps is 45,000 lumens. 45,000 / 12 = 3,750 lumens per square foot
Now for the big question. How much light do I need? The technology has advanced so much in the last 15 years that we are constantly refining the process and updating what we know works best for planting.
Current theory says that the minimum light needed to sustain growth is 2,000 lumens per square foot. The average would be 5,000 lumens per square foot. The ideal would be 7,000-7,500 or more per square foot.
To determine how much light you need in watts:
The general rule of thumb for setting the amount of light for an area is a minimum of 30 watts per square foot. 50 watts per square foot and ideal.
You can determine the amount of light for your area using this formula: 30 watts (or 50) X? (your area) in square feet. Example: You have an area of 10 square feet 30w X 10 s.f. = 300 watts / per square foot or 50 watts X 10 s.f. = 500 watts per square foot (ideal).
Remember that fluorescent lamps are weaker and emit less light than HIDs. This means that you will need 5 times more watts to match an HID lamp. So, 30 watts of HID would equal 150 watts of fluorescent.
Therefore, it is advisable to use a minimum of 30 watts per square foot for HID lights and a minimum of 150 watts for Fluorescent.
This is all very important as the intensity of the light will directly affect the quality and production of your harvest. If you have less than ideal, your harvest and potency will be reduced and the “shrimp” will not be as dense. This question is never too much to repeat. You must have the right amount of light for your space, to be able to harvest high quality “shrimp”.
The question can sometimes be, “Can I have too much light?” The basic answer is no. According to the law of diminished returns, you could theoretically reach a point where plants would no longer be able to absorb light, but it would be impossible to have that amount of light in your space. Heat would become a problem long before you reach that point. So use as many lamps as you can, just control the heat.
Experimentation is the only method to determine the best solution for each plant. If the plant is not receiving enough light, it will start to grow disproportionately as if it is stretching to seek light and the foliage turns pale green.
Or, if they need to be moved close to the light, or increased the period of exposure to light, they may have problems such as discoloring or burning leaves and flowers. Sheets can become super compact and curled at the ends.