Robotics Controllers Multipoint Digital I/O & 24Ch A/D & D/A (Commercial and Military)
Complex Waveform Generators (Commercial and Military)
16/24 Channel Electric Fence Detection and System Controller
Fast Prototyping and Concept Proofing (Lake/Ocean bottom Silt Level Detection)
Cellulose Ethanol Processing and Co-Generation
Hydroponic Lighting and Robotics
The Application of Light
A Little Background on Light
Sunlight and its exposure
Even though we are in Canada, the only chart I could find that gave a reasonable representation of light exposure rates was for the United States. The following map and tables gives some idea of how much light is ending up on the surrounding greenery.
U.S. Solar Radiation Watts per Square Metre Average (min/max)
(source: Energy Technics)
U.S. Solar Radiation Map
(source: Energy Technics)
How Much Light do you really get from HID Lamps?
Even though gas discharge lights are about the most efficient you can get for growing your crops (actually, they were until recently), they may not be as good as you think. Here are some charts of how much energy goes where (click on them for a larger image);
(source: Energy Technics) Not as terribly impressive as one might have hoped, for energy transfer levels into useable photons !
The following are the spectral response charts for 12 different types of lights; (source: Energy Technics)
What actually seems to make it almost an order of magnitude worse, is that 60% of the light actually radiated isn't useable by plants.
What kind of light do plants need?
That question isn't really that hard to answer. There is a reasonable body of documentation in books and on the web that gives the specific frequency of the light required for plant morphology with regard to increases in photosynthetic metabolic rates. In English the colour of the light you need to make the plants grow like crazy.
We, through our research, have tested the frequencies required and produced lights specifically tuned to generate those colours. I may get more into that area as time goes on. We are very close to releasing the new lights to the commercial marketplace. If you wish to see some of the results to date, please view the e-lights page.
Whenever you try to artificially stimulate plants into growth, you create problems. These problems, large or small, can be solved. But it depends on the effort you apply to the situation. High Intensity discharge lamps create large amounts of radiation. Most of this radiation, in the form of heat, and heat in this case, is our enemy.
There are three ways to get rid of unwanted heat;
1. Use Air Conditioning in your grow areas.
2. Use water jackets on your lights and smaller air conditioning in your grow area.
3. Use lights that don't create a lot of heat.
As examples of cooling and heating loading, I will use our standard 10 foot wide by 20 foot long by 10 foot high grow chamber. It's specifications are as follows;
Internal Area: 2000 cubic feet
Light type and qty: Philips 430w x 48
Water jackets: 24 Dual 430w
Energy Requirements: 29,562 watts (for lights only)
Number of plants: 1440 plants
Plant Canopy Height: 5 feet
90% heating load volume: 1000 cubic feet
Harvest Time: Daily
Harvest Rate: 96 to 144 plants per day
Growth Period: Programmable, 10 to 20 days
Our present system uses in total 1 ton of air conditioning and a roof top radiator based cooling tower for the water jacketed lights.
There are three ways you can plumb water jacketed lights, series, parallel or a combination of the two. Parallel plumbing of lights in systems using large numbers of jackets can be very complex and cost prohibitive from both an installation and maintenance standpoint. Each light has to have some form of regulating valve or orifice to insure equal flow occurs in all water jacket chambers.
A series arrangement removes the necessity of regulating valves. But the temperature difference of the cooling water can dramatically increase in temperature between the inlet and the outlet of the entire lighting system. In some cases by as much as 100 degrees Fahrenheit or 55 to 60 degrees centigrade. The only way to decrease the temperature differential is to increase the flow rate. Add a larger pump. But you don't want high pressure, you want a high flow rate. Water jacketed systems are normally low pressure and rated in the area of 2 psi to 5 psi. An example of a series system is shown at left (click for the picture for a larger view).
In the next case, we have parallel-series systems where a number of water jackets are arranged as columns of series connected units. Similar to the series system, water temperature differentials from one end of the chamber to the other end are extreme. In both cases, the higher the flow rate, the lower the temperature differential. An example of a parallel-series system is shown at left (click on picture for a larger view).
Of course, all of this hot water has to be cooled and recirculated. We certainly couldn't afford to run the system on tap water forever. There are again a number of ways to cool the water down from the jackets. The first we will examine is the single stage water to air heat exchanger.
Single Stage Water to Air Heat Exchange
This method uses distilled water and all plastic pipes and components. The radiator should be made out of high thermal conductivity plastic. A charcoal filter (house sized) is used on the front end to help collect materials leeched by the water. This generally increases component life and helps prevent mineral plating on the lamps. The primary drawback of a system like this is that all of the components must be plastic or stainless steel. A standard car radiator, although it will work, will eventually contaminate the water and cause mineral plating on the lights. A two filter system using a particle filter before the pump and a charcoal filter after the radiator might help to some extent. But unless the radiator is made of stainless steel or plastic the system will corrode and fail.
Two Stage Water to Water to Air Heat Exchange
Here we use a clean distilled water loop traveling through a heat exchanger. In the heat exchanger we circulate water/glycol which absorbs the heat from the distilled water and then dumps the heat through any standard car or truck radiator (system size dependent). In this case the water in contact with the lights is in its own closed system and should be at slightly higher pressure in the heat exchanger than the water used for heat transfer. The reason for this, is that if there were ever a leak, it is better to leak distilled water out than glycol in and cause mineral plating on the lights. These systems are easy to build and highly maintainable.
Two Stage Water to Mass Water Body Heat Exchange
This system, as in the above, uses a heat exchanger to isolate the distilled water cooling the lights. In this case however, we use the water in a pool, pond or other body of water to act as the thermal energy dumping ground. One component not noted but required if you are using a pond, is a filter on the inlet of the pool side of the heat exchanger. You don't want fish or other materials being pulled into the heat exchanger and reducing its effectiveness.