“Fiat Lux,” Latin for “let there be light,” is the famous quote that begins the third verse of Genesis. We all know that plants need light to carry out photosynthesis and the best (and cheapest) way to get it is to use natural sunlight. Alas, that is a luxury many of us don’t have. We are relegated to growing our plants indoors; in closets and cubbies, in basements and bedrooms. So for us, what is the best way to light our gardens? We have several options: Fluorescents, HID (Metal Halide or High Pressure Sodium), Plasmas, and LEDs. What basic grow light information do we need to know when we choose how to light our garden(s)? First we need to know what our obstacles are…
One of the biggest problems we as indoor gardeners face is that most of our lighting options produce heat, a lot of heat; approximately 3.4 BTU (British Thermal Units) per hour/per watt. That means that a single 1,000 watt HPS light system generates 3,400 BTU of heat every hour. A BTU is the amount of energy required to raise 1 pound of water 1 degree Fahrenheit. To give you an idea how much heat that is; each 1,000 watt HPS light radiates enough heat into a grow room to boil 3 gallons of water an hour!
Another obstacle for indoor lighting is the penetration of light through the plant canopy. Light diminishes from its source with distance. The relationship of light emitted from a point source (a bulb) and distance is known as the inverse square law. The law states that the intensity of light changes in inverse proportion to the square of the distance or I (intensity) = L (light) / D (distance.) That means that the intensity of light 2 feet away from the source is 25% of the intensity 1 foot from the same source.
The last challenge of indoor grow lights is that most lighting requires huge amounts of electricity. In order to cover a 10’ x 10’ room high light plants require 4,000 watts of lighting or more. The average American household uses 14,000 watts of electricity per day according to the Department of Energy so the above mentioned garden would account for 28.6% of their total electrical consumption. Use this handy electrical usage guide to find out how much your electricty will cost per month. With the cost of electricity ever on the rise the search for more efficient horticultural lighting has LED down several roads… Check out part 2 of this blog series for a review of different types of horticultural lighting and how they stack up.