The difference between these two types of HID (High Intensity Discharge) lights is the color spectrum that is emitted from each. The High Pressure Sodium bulb emits light that is concentrated in the red to yellow side of the spectrum and are weak in the blue-violet end. While the Metal Halide bulb emits light that is very balanced and contains all the energy peaks at wavelengths of the visible spectrum. Visually the Sodium bulbs will appear very yellow-orange and the Halide bulbs will appear more blue-white in color.
The Halide lights have a very balanced spectrum and are excellent for vegetative growth or leafy plants like lettuce and basil. The Halide lights produce between 65-115 lumens per watt which is a measure of the efficiency of the bulb, or how much light you are producing for the amount of electricity you are using. The Sodium lights produce light that is very bright and concentrated on the yellow to red side of the color spectrum. This color is not as balanced as the Halide but makes up for the lacking of a balanced spectrum in the amount of light given off by the bulb. The Sodium bulbs produce between 97 to 150 lumens per watt which is much higher than the Halide bulbs. The Sodium bulbs are superior in life expectancy and efficiency while the Halides a superior in spectral distribution so your decision will be based on what is more important to you.
Many people switch between bulbs for different stages of growth for a couple of reasons. First of all, Sodium bulbs have been known to make some plants grow leggy and stretched out because of the yellow to red spectrum that they give off. Metal Halides tend to keep these plants tighter with less space between internodes. So some growers use the Metal Halide lights during vegetative growth to keep the structural growth of the plant nice and tight. But they switch to Sodium lights when the plants begin to flower because the Sodium lights produce so much more light than the Halides. Even though the Sodium’s do not have as good a spectrum as the Halides the intense light that is put off by the Sodium’s aids in flower development and fruit set. Do not be fooled though, you can use either light throughout the life of a plant and get excellent results.
The first thing you need to do is figure out what kind of square footage you are dealing with. Do not just figure for the whole room figure out what the plant area is that you need to cover and multiply length x width to get the square footage. Now, you will want to try and achieve at least 30 watts per square foot. So if you have a 4 x 4 area which is 16 square feet and you multiply by 30 watts, you get 480 watts. So for a 4 x 4 area you will need to use at least a 430 watt light. Remember though that the amount of light required will depend on the plants because some plants like lots of light and some like low levels of light.
Yes. A ballast is required to start the lamp and to increase the voltage required to run the lamp. The ballast is responsible for starting the lamps by providing a high, fast charge of electricity. After the bulb lights, the range of voltage and current are controlled by the transformer which is why the bulbs operate so efficiently.
Yes, very efficient compared to standard incandescent bulbs found in your house. For example one 1000 watt sodium bulb produces as much light as about 87 standard 100 watt incandescent bulbs.
HID light bulbs come in a variety of spectrums and strengths to meet the needs of indoor gardeners. The lumens and PAR (photosynthetically active radiation) levels drop quickly. You can check this for yourself by measuring your yields with new bulbs versus bulbs that are 8-12 months old.
The newer bulbs in the same environment should offer noticeably larger yields over the old ones. After 8-12 months of continuous use, the bulb should be replaced.
There is no energy savings from running your lights at 240 volts. That is a misconception that many people have. The main advantage is the fact that you can run more lights on one electrical circuit. For example if you run a 20 amp 120 volt circuit, you can only run two 1000 watt lights on that circuit. If you were to wire the circuit up for 240 volts you can run four 1000 watt lights on that circuit. This makes for a lot less wiring but does not save you on your electricity bill because each light still uses the same amount of watts.
More often than not the main difference between high end lights bulbs and cheaper ones is just the reflector. High end reflectors are designed to create more of a spread for both its light output and heat while budget reflectors typically don’t do as good of a job at dispersing light and heat.
No. You should never interchange bulbs between systems unless they are specifically made to do so. Lots of people ask if they can use a 250 watt bulb in a 400 watt system and the answer is definitely not. You could put yourself at risk by doing something like this because the bulb could become unstable and explode. You should also never put Halide bulbs in a High Pressure Sodium system because the ballast’s are only meant to run the type of bulb they are rated for and a Halide bulb in a Sodium system could overheat and explode also. There are conversion bulbs manufactured that are High Pressure Sodium bulbs that are meant to run off of a Halide ballast. But once again only put the bulb in a system it is rated for.