High Pressure Sodium Lights are good for indoor gardening and hydroponics.
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Q: Can I use a High Pressure Sodium Light all the way through on my Blooming, Fruiting plants?
A: America is a free country. You can do anything you can afford.
Q: What will the results be if a High Pressure Sodium Light is used from start to finish on Blooming Plants?
A: The coloration of a High Pressure Sodium Light is similar to Autumn sunlight, lower on the horizon. This often causes the plant to grow in a "hurry-up" form; the leaves are smaller, there is more spacing between the leaves, and the plant looks stretched. Sometimes this is a problem, sometimes it is not. If the High Pressure Sodium Light is shining along with Natural Sunlight, the effects are less pronounced. Just like everyone else who sells grow lights, we will always tell you to buy another one, but if one light is all you have and can afford just go with it, OK?
Q: What about those 60 or 75 Watt Sodium lights they sell at the hardware store? They cost a lot less.
A: Those are Sodium lights, yes, but they are Low Pressure Sodium.
Q: What's the difference?
A: There's two differences that count for plants. The first is that the spectrum or color range is not really usable by the plants and the second is that there really isn't enough power to overcome the limitations.
Q: The Low Pressure Sodium color looks the same as the High Pressure Sodium.
A: You're right. A High Pressure Sodium light is actually not a real good color for plants either. The only reason it works for growing plants is that the power is just so strong it throws enough light from the good frequencies or colors to make up for it. A Low Pressure Sodium light hardly has any good frequencies or colors and it has no power to push the light into the plants. In fact, if all you shine on a plant is a low pressure sodium light, the plant can die. This is only in case a low pressure sodium is the only light it gets.
Q: What about Fluorescent light tubes? They cost a lot less.
A: Fluorescent light tubes can work OK--but only up to a point.
Artificial light fades fast. The tubes must be put very close to the plants--often two to four inches. Each four foot tube uses 40 Watts; a fixture with two four foot light tubes uses 80 Watts total. This is 20% less than a 100 Watt HID light.
A 100 Watt Metal Halide is rated at 9,000 initial lumens; fluorescent tubes can range from 1600 to 2600 rated initial lumens per tube. In theory, using these numbers, two tubes will give you somewhere between 3,200 to 5,200 initial lumens.
Now, let's stop before we go any farther with an analysis of these numbers. Initial lumens is just a guide. It is measured right next to the bulb and it the absolute highest possible value that can be obtained. For example, on a four foot fluorescent tube, the amount of light is going to be highest in the center of the tube and some what less at the end.
Q: How much less?
A: These numbers are just guides. If you set up all the equipment needed to measure the actual amount of light you would get in a real set up in your house, the numbers would be all over the board. The measurements would vary from day to day, from time of day, how long the lights have been on, how old the bulbs are, any stray light, time of day of stray light, season of the year of stray light, and on and on and on.
Q: You just aren't going to put any numbers on that, are you?
No.
Q: OK, so what do you know?
There are 9,000 initial lumens from the 100 Watt Metal Halide and say 4,900 initial lumens from two fluorescent tubes. That works out to be 90 lumens per Watt for the HID versus 61.25 lumens per Watt for the fluorescents. You can call this one third more efficient in the use of electricity.
Q: So, the HID is more efficient.
Well, maybe. In theory, just based on output--you get more light per Watt.
But that's not the only consideration. It depends on what you are doing. Fluorescents are great for starting seedlings. One reason is that the fluorescents spread the light over a differently shaped area and very small seedlings do not need a whole lot of light. Blue fluorescents are usually your best bet for starting seedlings since the warmer, red light is mostly for budding and blooming and most folks do not bud out seedlings. In practice, after about two weeks, the seedlings have done about as much as they are going to under the fluorescents. If you want to keept he plants growing indoors, it is time to move on to the HID. You will never get a tomato or pepper to yield good fruit under fluorescents.
Q: What if I add more fluorescent tubes?
Four tubes use 160 Watts, eight tubes use 320 Watts, twelve tubes use 480 Watts, twenty-four tubes use 960 Watts. You will get much more efficiency and a lot more light from similar Wattage HID lights. Don't forget--artificial light fades fast.
The best way to artificially light a plant is to give the plant a balanced range of light at a good power range for the size of the leaf space.
If you can give the plant a few hours of natural sunlight a day, the plant receives a good mix of the color spectrum. Especially in winter, the number of hours of good sunlight are limited; this is even more true the farther North you live. It is simply not practical or affordable to try to match the sheer power of the Sun.
Artificial Light fades fast.
A High Pressure Sodium Light is a great tool to grow blooming, fruiting plants. The orange-yellow color range encourages plants to set fruit or bloom. You can gain a good deal of control over when your plants bloom or set fruit as well as simply encouraging your plants to bloom and set fruit by using a High Pressure Sodium Light.
