Al great to see you back around, much respect for all the valuable knowledge!
Are your feelings still the same towards electric(digital) ballast? As in its still not worth the ridiculous amont of dough.
When every I see a question about are digi's better I always give them your quote. The one where you did a test in your local shop and found that they put out the same lums as a good ol standard magnetic ballast. Even though lumatak says their ballast produce 30% more blah blah blah bs bs exc......
They've even made types now that can go from 400/600 just with a flip of a switch just like a hps/mh switchable. Wouldn't it be safe to say that even if you did have it running on the 400 wouldn't it still be using just as much energy as it would if it were on 600watts?
I've been away from commenting on this sort of thing for long enough that I thought it would bear fruit to go looking around to see what I've missed. Strangely enough, nothing's changed in my absence.
As regards the Lumatek 400/600 ballast, yes, you can run either wattage HPS lamps off one but you will have to have BOTH a 400HPS lamp to run the ballast at 400W and a 600W HPS lamp to run it at 600W. You can
not crank up a 400W HPS bottle to 600W.
Due to the nature of operation of HPS lamps, it's the characters of the lamp itself in operation which sets the conductivity hence the power rating of the lamp. If you connect a 400W lamp to a 600W ballast, the ballast will apply a 1.5x higher voltage to the lamp tube than it is designed for- and the result will be about 30s of operation (if you're lucky) before the lamp tube catastrophically fails. The quartz tube within the borosilicate glass envelope will crack, pressure will be lost and the lamp will stop emitting light. If you're lucky, the quartz tube won't explode with quite enough force to shatter the envelope, but if you're not lucky, you'll end up with bits of glass, quartz and mercury/sodium amalgam all over the place.
Having said that, I suppose it's going to be tremendously convenient for some very few users to be able to switch between 400 & 600W, but they'll still require 2 lamp tubes.
Lumatek say that some models of their ballasts are dimmable; you can dim a lamp to 50% of normal rating- but.. why... the... fuck... would... you... want... to...?!
The '30% greater lumens' is still nonsense. The luminous output of an HPS tube is a function of how much power (in watts) is dissipated across the tube. You can increase the wattage dissipated in the tube if you increase the supply voltage. However, this will cause the thermal dissipation within the tube to exceed the design's limitations and will reduce the life of the tube. So, how do Lumatek substantiate their '30% more lumens' claim? They can't. If you connect a sample 600W HPS bottle to a Lumatek ballast and measure light output with a lux meter, you're going to get the very same luminous output as you do with a standard magnetic ballast.
Now... if Lumatek shift the goalposts & claim '30% more lumens/tube lifespan,' the waters become murkier. HPS lamps naturally lose luminous output with ageing. Electronic ballasts start the tube a bit more gradually, which consumes the Hg/Na amalgam more slowly, meaning the tube will strike more times over its lifespan, potentially giving more lumen/hours of useful operation. This probably is useful if you're an operator of municipal street lighting, where you don't really care if you're getting 100% of rated luminous output or 80%. You might get another year of operation with a ballast that 'soft-starts' the tube. Mind, horticultural HPS tube makers recommend tube replacement every 12 months- because horticultural users DO care about the degradation of luminous output with tube ageing. Electronic ballasts are probably a very good thing for streetlighting operators- that is, if they can justify the 2-3x cost of an electronic ballast over a standard magnetic type against savings in reduced tube replacement frequency and power cost savings.
Electronic ballasts don't have iron-cored inductors. Iron-cored inductors have inherent eddy current losses which generate heat in their laminations, so they're less efficient. A standard magnetic 600W ballast will draw about 695W in operation, after tube warmup. If Lumatek's figs are to be believed, their 600W ballast will draw 615W. The 80W is significant, but significant enough to justify the 2-3x higher purchase price of their product? My local hydro shop sells 600W magnetics for $120, 600W Lumateks for $360, a difference of +$240. How long would it take to recover the extra $240 cost of the electronic ballast? At my local (very high) rate of 19c/kWh an 80W draw costs $0.0152/hr (1.5 cents/hr), it'll take 16,000 hours for me to recover the additional $240 spent on the electronic ballast in power savings. A lamp used in a 12/12 flowering application runs about 4000hrs/yr, so the payback time is about 4 years. I have a friend in Tennessee who is paying about 5c/kWh for electricity. In that person's case, the payback time is roughly
16 years. Woohoo, let's hear it for power cost reduction!! *applause*
Poor quality magnetic ballasts don't have securely bolted inductor laminations. Over time, they'll become noisy- if they're not already noisy when new. Good quality ballasts are silent from day 1 and remain so for many years. My 1000W ballasts are now about 12 yrs old and are still silent. Anyone who whinges about noisy magnetic ballasts apparently has never owned a good quality magnetic ballast.
As regards heat dissipation from magnetic ballasts- yes, there's a significant amount of heat generated by eddy current losses in the iron inductor core. This can be a problem for some users. So, you mount the ballast outside the grow room airspace... problem solved. However, in some cold winter weather localities, having a little heat from a ballast dissipated into the grow room airmass is a very helpful thing, particularly in winter.
I've been an electronics techie for more than 30 years. I have YET to find a semiconductor junction which is as durable as a coil of copper wire wound on an iron core. The useful lifespan of magnetic ballasts is measured in DECADES. If you buy a good quality magnetic ballast, it's reasonable to expect that it may be the only ballast you ever buy. Lumatek warranty their ballasts fully for 3 years. After 3 years, there's an additional 2 year pro-rata warranty, where you will get partial credit of the purchase price in case of failure. Any questions?
So, are electronic ballasts worth the dough? Same luminous output, despite mfr claims. Lower power consumption, but many years to recover the much higher purchase price compared to magnetic ballasts. Yes, Lumatek ballasts have a 3 year full value replacement warranty, but what happens when one fails? You'll have to return it for repair or replacement, but how long will your grow room be dark in the process? As cheap as magnetic ballasts are, it's economically practical to keep a spare ballast on hand, meaning zero downtime.
In the net analysis, magnetics are simply more practical.
might that be the weak link? either way 
