If it's more info you want, here you go, something I copied from one of the hydro supply shops, One thing I didn't realize is the fact that if there is a short the ballast will shut itself off, minimizing the risk for bigger problems. I think that holds true for most switching power supplies which I believe digitall ballasts are.
Digital Ballasts
The days of the old humming, magnetic core & coil-type ballasts may soon be coming to an end. The digital (electronic) ballast is the latest in ballast innovation. Digital ballasts are more efficient, quieter, cooler, and softer on the bulb. Digital ballasts do not have any of the usual transformers, capacitors or igniters; instead these ballasts have electronic circuitry to do the same job, more efficiently. What might take a standard coil/magnetic ballast 680-700 watts to fire a standard 600 watt bulb, may only take a digital ballast only 600-620 watts to fire the same bulb to the same brightness. The old coil type ballasts are hard starting ballasts; when the ballast fires the bulb it sends full power to the cold bulb. Over time, this shortens the bulb life and reduces the PAR output of the bulb. Digital ballasts start by sending a low amount of power to the bulb and steadily increases the power over the next few minutes until the bulb has reached full brightness. This is also known as soft starting, which minimizes the damage to the bulb and increases its PAR life (PAR represents the plant usable light; its what plants see and use, versus lumens which are what people see). After one year of use the plant usable light coming from bulbs that are run on digital ballasts has decreased only by 20-25% where as the same bulb being used in the coil type ballast would have lost 50-60% of its plant usable light over the same period of time.
Coil type ballasts are also known to cause the bulb to flicker or strobe. This takes place so quickly that the neither human eye nor light meter can pick it up. Digital ballasts provide a uniform power supply to the bulb, thus eliminating the flickering from the bulb.
A great feature of digital ballasts is the ability to run both MH and HPS bulbs on the same ballast without having to flip a switch (it should be noted that not all digital ballasts on the market are programmed (or optimized) to do this properly). Digital ballasts are intelligent ballasts and most are able to recognize the difference between the two types of bulbs and fire them accordingly. Because of the high starting power requirements of some bulbs (such as the Solarmax) digital ballasts cannot always fire these bulbs due to the soft starting feature inherent to digital ballasts. Nor do digital ballasts fire multi-vapor bulbs. The good news is that the majority of bulbs in our industry work just fine with digital ballasts. However, a great safety feature of digital ballasts also help to prolong the ballasts life. If the bulb is defective or incompatible and does not fire, the ballast will only attempt to fire the bulb after a predetermined amount of time and shutdown if unsuccessful. Digital ballasts will also shut down if there is a short in the system. When purchasing a digital ballast, the consumer must be aware that there are a few black sheep in the digital ballast family. There are many inferior quality digital ballasts on the market; these manufacturers proclaim amazing power savings but dont deliver. BetterGrow Hydro has looked at numerous digital ballasts over the past several years and we have settled on the Lumatek brand for specific reasons. Below are the results of our in store tests with various brands of ballasts. Gathering data was conducted using a wattage meter and a Hanna Light Meter, both of which are available to our customers should they wish to purchase these meters and run their own tests. The Hanna Light Meter was placed 29 from a Hortilux bulb and the lumen reading was taken once the bulb had reached and maintained full brightness. Here are the results from a few of our tests:
Results
*note: the 750W Lumatek was run at 220V; the amperage would have been almost double if it was possible to operate & test at 120V
Detailed Results
600w Lumatek (120v)
Watts: 610w - 620w
Amps: 5.1A - 5.15A
Light Output: 12.26
Efficiency: 50.6 (Watts/Light output)*
Time until full luminance: 2 minutes
Bulb: 600w HPS Hortilux @ 29"
600w Galaxy (120v)
Watts: 590w - 600w
Amps: 4.95A - 5A
Light Output: 9.71
Efficiency: 60.7 (Watts/Light output)*
Time until full luminance: 2 minutes
Bulb: 600w HPS Hortilux @ 29" (stopped firing bulb after 2 min on first attempt)
750w Lumatek (240v)
Watts: 750w (taken from ballast)
Amps: 3.38A (derived calculation)
Light Output: 14.9 (Power Source was 220v)
Efficiency: 50.3 (Watts/Light output)*
Time until full luminance: 3 minutes
Bulb: 750w HPS Super @ 29"
1000w Evolution (120v)
Watts: 1010w first 2 min - 850w after 4 min
Amps: 7.8A - 8.2A
Light Output: Peeks at 16.7 (2 min) then drops to 14.7 (4 min)
Efficiency: 57.8 (Watts/Light output)*
Time until full luminance: 2 - 4 minutes
Bulb: 1000w HPS Super @ 29"
Notes: Fan is louder than the humming of the SSX ballast!
1000w Sun System 6 (120v)
Watts: 1080w - 1100w
Amps: 9.6A
Light Output: 18.6
Efficiency: 59.1 (Watts/Light output)*
Time until full luminance: 6 minutes
Bulb: 1000w HPS Super @ 29"
*lower is better
An important aspect to note from the above results is that the digital ballasts that run on low power also emit less light. While this may help out with the power bill, it is disastrous for your plants. The actual efficiency of some of these ballasts is worse than the old coil ballasts.
Another observation was that the Galaxy ballast seems to have a problem firing a new bulb for the first time. After firing a new bulb for two minutes the ballast shuts down and stops firing the bulb. Once the ballast has fired the bulb for the first time, however, it is able to fire the bulb the second time and maintain the power to the bulb. The Galaxy was also the least efficient out of all the ballasts in converting electrical power into light; even the 1000w coil ballast was more efficient!
The 750w Lumatek ballast produced more light than 1000w Evolution; this was true even though the Lumatek ballast was powered by 220v and not the required 240v. We also found that the light intensity on the Evolution decreased further after 30 minutes of operation.
It should be noted that Hortilux bulbs (which we used for many of our tests), while having a good spectrum, have a relatively low lumen output. Had we used a standard bulb (such as a Philips or Sylvania) the output ratings undoubtedly would have been higher.
The last point we would like to make here is the fact that after 2-3 years of operation (sometimes less), coil ballasts begin to degrade in performance and generate even less light than when they were new; digital ballasts do not experience this decrease in performance.
RF Interference
The next test was to measure RF interference. To do this we first placed the ballast at four feet from our radio and gave a rating according to the amount of interference for both FM and AM radio stations. Then the ballast was then placed 30 feet from the radio and the same process was repeated. Our results are as follows
4ft AM 4ft FM 600w Lumatek Moderate Interference.
none
600w Galaxy Extreme interference (Cannot hear radio transmission) when bulb fires (lasts about 30 seconds), Once bulbs has fired and the lamp is being maintained RF interference is High (Can hear radio broadcast but with considerable static).
none
750w LumatekModerate Interference for 2-5 seconds while the ballast first fires bulb. No interference after bulb successfully fires.
none
1000w Evolution Moderate Interference
none
30ft AM 30ft FM 600w Lumatek Slight interference (Radio broadcast is clear with a slight amount of interference in the background).
none
600w Galaxy Slight interference (Radio broadcast is clear with a slight amount of interference in the background).
none
750w Lumateknone
none
1000w Evolution Slight interference (Radio broadcast is clear with a slight amount of interference in the background).
none
Customers should avoid all digital ballasts that do not have RF shielded lamp cords. The RF interference from these digital ballasts is substantial. If you do not see a metal shield between the outer coat and the wires on the inside of the lamp cord, the cord is not shielded. Digital ballasts do not interfere with FM radio stations but do cause static on AM stations. The better quality digital ballasts, such as the Lumatek, cause the least amount of interference. It should be noted here that the 750w Lumatek ballast we tested was of their latest revision. Ironically, this revision does not utilize an RF shielded lamp cord; Lumatek claims that this is due to internal changes made to the ballast that make the RF shielding unnecessary, and as you can see by the test results, it produced virtually no interference after the first few seconds. Lumatek claims that all of their ballasts will utilize this same construction in the near future.
Regarding out Testing
BGH ran these tests in an effort to address the tons of questions we receive each week from our customers regarding digital ballasts and their true performance versus their stated performance. The tests were not designed in any way to slander some manufacturers or promote others. The problem that we, as well as our customers, faced was that every ballast manufacturer whose ballast we have tested over the years had made claims that were either exaggerated or simply not true. The only way to know for sure was for us to conduct the tests ourselves. Granted, we did not have access to some of the expensive equipment that the manufacturers did, but what we have found is that you can use certain equipment to run certain tests on a certain ballast to produce results that look favorable or poor, it just depends on how the tests are run, what criteria is used, etc. Obviously, if a manufacturer runs a test and doesn't like the results, they are not going to advertise them. They may, however, run a different test and if they like those results publish those instead. The point is, there are many different ways to skin a cat when it comes to testing digital ballasts, and we just used the testing scenarios that were available to us (look, you can have the most expensive RF interference testing equipment available that tells you a ballast is clean, but if you turn on a radio 30 feet away and experience interference, thats got to tell you something!).