HID lighting: a Breakdown
What is HID Lighting:
HID stands for High Intensity Discharge, referring to the discharge of light that occurs when you run electrical current through the gasses contained inside the arc tube. There are many different kinds of HID lights, the three most often found in the garden are High Pressure Sodium (HPS), Metal Halide (MH) and the relatively new Ceramic Metal Halide (CMH) . All three of these kinds of bulbs emit light by running electrical current through gasses, but they differ mostly in the kinds of gasses inside the arc tube, and the material the arc tube itself is made of. These two factors determine the quality of the light, and how long the bulb lasts.
For all kinds of HID light – the arc tube is sealed completely, and the gasses inside are a combination of varying levels of Metal Halide salts and certain elements such as Mercury, Sodium, Krypton, Xenon and Argon to name a few. These molecules of gas get excited when you run current through them, causing them to emit light and move around in a rapid motion, beating against the inside of the arc tube, over time leading to it’s degradation, hence the reason they must be replaced so often. Quartz glass arc tubes like the ones on traditional MH fixtures can’t stand the same intensity that a ceramic arc tube can. For this reason, they degrade much quicker.
All HID bulbs operate on the same basic principle, but the different colors of light come from the different ratios of gasses inside each bulb. For example an HPS bulb has more sodium than a MH lamp. Sodium emits a yellowish-red light, that’s why High Pressure Sodium light has a yellow Hue. Regular Metal Halide lamps have more Mercury and Metal Halide salts which emit a more blue-ish light, and less sodium, that’s why their light is bluer. Metal Halide bulbs can be tweaked to be different colors, either 4K 6K 12K or anything in between, but high pressure sodium bulbs are usually 2K, no matter what brand. Since the gas in an HPS bulb is always mostly sodium, the color is similar even among different brands.
What you need to know about HPS:
High pressure sodium lamps are used almost exclusively for flowering, though some folks use them in the vegetative stage as well for safety reasons. High pressure sodium arc tubes operate at a much lower atmospheric pressure, meaning if the arc tube cracks, there is no explosion, so they are generally considered to be much safer than Metal Halide. High pressure sodium bulbs generally last longer than Metal Halide bulbs as well, thus needing replacement less often.
High pressure sodium lights were originally designed to be used as streetlights. The light from sodium gas peaks around 555 nm, which is a yellowish-red color. That wavelength is absorbed by the human eye more efficiently than any other, so naturally it was chosen for the street light application. It was later discovered that plants also flower well under this color of light, and High Pressure Sodium is now considered the most trusted, tried and true flowering bulb in the industry.
What you need to know about Metal Halide:
Metal Halide bulbs are used by horticulturists for a wide variety of applications including cloning, vegetative growth and flowering. Metal Halide bulbs are generally full spectrum, containing varying levels of mostly blue and UV light, so it matches the color of the sun better than most lighting applications, making it very diverse! They were originally designed to replicate daylight in the summer time so they are great for aquariums, horticulture or industrial lighting. Most horticulturists use them during the vegetative stage, though some growers flower with Metal Halide as well.
Metal Halide gets its light blue color from the highly reactive gasses inside the arc tube. Unlike High Pressure Sodium, Metal Halide bulbs contain a diverse group of gasses including Krypton, Argon, Xenon, Mercury and others. Bulb manufacturers tweak the exact ratios of each gas inside to get different colors of Metal Halide light, like the 6K Metal Halide or the 10K Metal Halide. As a result, bulb manufacturers have over time been able to tweak Metal Halide bulbs to the exact colors they want, which is why they have been able to so closely match sunlight.
Because of the intensity of the highly reactive gasses inside the arc tube, Metal Halide bulbs need to be used with caution, and replaced more often. Responsible growers remember to replace them as often as the manufacturer recommends to avoid bulb failures!
What you need to know about CMH:
Ceramic Metal Halide bulbs use ceramic arc tubes instead of quartz glass arc tubes to produce higher quality light. The ceramic arc tubes can withstand more pressure than quartz glass ones, so manufacturers are now able to fine tune the spectrum even more precisely than before. By fine tuning the gasses even further, we are able to produce more PAR per watt and a fuller spectrum. Ceramic arc tubes are more resistant to breakdown, so they last longer than MH and HPS bulbs, saving growers’ money in the long run.
The CMH lights are designed specifically for horticulture, so plants generally show faster, more vigorous and healthier growth under the CMH lights. The CMH bulbs give off a much more rich and full spectrum light, so plants don’t have to stretch to get certain wavelengths of light they may be looking for, (as is often the case with HPS.) For this reason, plants grown under the CMH exhibit shorter, bushier growth with more flowering sites and denser flowers. It is understood by experts in the industry that the CMH light is generally better than both HPS and MH. This technology is new and many folks don’t know about the benefits of CMH bulbs yet, so expect to see more in the future!
What’s the difference between a Ceramic Metal Halide and regular Metal Halide Bulb (MH)?
Ceramic arc tubes offer a number of advantages over quartz glass arc tubes. For starters, they last longer. It has been discovered that much like the case with brake pads, ceramic is simply a better material for the job. Ceramic HID bulbs, when run at the recommended wattage and frequency, last on average twice as long as an HPS bulb, and about 3-4 times longer than a regular MH bulb.
Quartz glass arc tubes like the ones on traditional MH fixtures can’t withstand the same intensity that a ceramic arc tube can. For this reason, they degrade much quicker and have a shorter usable life. The only disadvantage to using ceramic tubes is that since the technology is so new, a lot of lighting companies haven’t developed fixtures for these kinds of bulbs, meaning we are limited on versatility in the grow room. The other disadvantage is the higher cost – however this is negated by the fact that they last twice as long, and thus need to be replaced half as often, saving you money over time.
Question and Answer
Q: It’s hot, and I have to dim my fixture down to 600 watts. Do I need to buy a new 600 watt bulb, or can I still use my 1000 watt bulb and just dim it down?
A: Most 1000 watt ballasts and 1000 watt lamps operate at 220v lamp voltage, however most 600 watt ballasts and 600 watt lamps operate at only 110v lamp voltage. This voltage is referring to the voltage the lamp is being operated at – not the voltage coming from the wall. Consult your ballast manufacturer to determine which voltage of bulb you need, keeping in mind for a 1000w ballast you will almost always still need a 1000 watt bulb, even if you plan to dim it down. This is important – operating lamps on the wrong voltage WILL decrease lumen output, decrease usable life and can have trouble igniting.
Q: What kind of fixture do I need to run a Grower’s Choice 630w CMH DE?
A: The Grower’s Choice 630 DE CMH operates best in a low frequency square wave ballast. Many growers are having issues with heat so they are dimming their fixtures down, and many other growers are switching to CMH because the richer spectrum is much better for plants, giving better yield. Utilizing these bulbs in a standard DE fixture is a great shortcut which achieves both of those goals, greatly minimizes operating expenses and grows higher quality flowers. However, it should be understood that since DE CMH bulbs were designed for low frequency ballasts, a few users may experience longevity issues in certain brands of high frequency ballast. However, we believe the amazing added benefits of the full spectrum combined with the money saving opportunity in utilizing your existing fixture far outweigh the risk of an early bulb failure, and we are developing a ballast right now that is designed specifically for our DE CMH Lamps.
Q: Should I use an open hood or an enclosed one?
A: Depending on what type of bulb you are using and what state you live in, you may or may not be required to have either a double jacket or a secondary layer of protection in case of a burst. Stricter commercial states like Colorado and Washington have regulations pertaining to the use of double and single jacketed as well as the use of open and enclosed hoods. Failing to follow regulations can lead to legal trouble and insurance claims being denied, so it is important to contact your local authorities to find out what the regulations dictate BEFORE you begin planning your grow.
Q: I can run the DE CMH at 600 watts or 660 watts, but can I run this lamp on 750w?
A: No. 750w is almost 20% more than 630w. 20% is too much! As a general rule, overpowering ANY bulb by more than 10-15% is a bad idea. This will decrease the life of the bulb, decrease spectral quality and could void the warranty.
Q: Why is a full spectrum better for plants?
A: It is commonly believed that plants use only red and blue light for photosynthesis but this is simply not true! Giving your plants a full spectrum light prevents them from having to stretch for certain wavelengths that may have been drowned out by the intensity of another wavelength. For example, under HPS light, your plant will need to search for more red and blue because it is being blasted with yellow and by the time you get the light far away enough from the plant not to burn it some wavelengths don’t have enough intensity for optimal growth. CMH lights do a better job of striking your plant with equal amounts of all the necessary wavelengths of light, which is why CMH lights allow your plant to grow short and bushy with plenty of flower sites per square foot, increasing yield.
Q: How often should I replace my lamps?
A: Savvy Growers replace their lamps often in order to maximize production and maintain steady results. 10% degradation may not seem like a whole lot, but there is almost a direct correlation between lamp life and yield, meaning if your lamp life is at 90 life%, you are sacrificing about 10% of your yield. Oaksterdam University recommends changing your lamps every 2-3 grow cycles for maximum production and consistent results.