Let me present some basics of ballasts for HID lighting, and hopefully it can be related to what Frank said, and explain what he is doing.

The ballast provides the proper starting voltage, operating voltage and current to the lamp to initiate and sustain the arc. HID lamps have a negative resistance characteristic, which causes them to draw an increasing amount of current, hence need a current limiting device. The ballast provides these functions. There are several different ballast types used for for HID lighting. Basically, there are two primary distinctions between ballasts: "lag circuit" and "lead circuit" ballasts. The current in lag type ballasts is controlled by an inductive resistance in series with the lamp, whereas in lead type ballasts it current control is provided by both inductive and capacitive resistances in series with the lamp.

Now these, lag and lead type circuits can be created in several different ways, each with thier own characteristics and pros and cons.

The simplest lag circuit, is a single core and coil placed in series with the lamp - this is called the NORMAL POWER FACTOR ballast. Note, there is NO capacitor used in this circuit. THe problem with this type of circiut is that the power factor is about 50% lagging, hence the name normal or low power factor. This type of circuit tends to be sensitive to fluctuations in line voltage, and is not recommended for fluctuations more than 5%. The line current at starting conditions is also approximately 50% higher than normal operating current.

To improve the power factor of the circuit, a capacitor is connected across the input lines. The capacitor's main function here is to correct the power factor, increases it to around 90%, and reduces the starting current draw, hence allowing more ballasts to be run on the same circuit. Note that the capacitor does not affect the lamp circuit.

CWA - Constant Wattage Autotransformer is another circiut used in ballasts. This is a lead type circuit and is used in most modern mercury lighting systems. This ballast type consists of a high reactance autotransformer and capacitor in series with the lamp. Unlike the two circuits mentioned above where the capacitor only serves to provide a correction to the power factor, the capacitor here forms an important ballasting function, and allows the lamp to operate with better stability under fluctuating voltage conditions. It is the most efficient circuit, and hence most popular.

The circuits mentioned above are used primarily with mercury vapor lamps. The Iwasaki lamp is designed as a replacement for mercury vapor lamps, and hence requires a ballast suitable for mercury vapor lamps. The ANSI designation of mercury vapor ballasts for 250W lamps is H-37 and for 400W is H-33. So in theory, any ballast with the H-33 designation should drive a 400W Iwasaki lamp.

MH ballasts, perform much like the CWA ballasts for mercury lamps, and have the ANSI designation M-58 for 250W and M-59 for 400W. Often, you will find that the ballasts used for aquarium lighting have dual rating M-58 & H-37, M59 & H-33. Hence these ballasts can be used for both MH and MV lamps. But remember that these are CWA ballasts.

Now the Iwaski lamps, in the pamphlet that comes with the lamps, says "250W Reactor or Autotransformer type Mercury ballast without peaking capacitor. Do not use on Regulator (CW and CWA)" They recommend a High Power Factor ballast - Advance Transformer ballast - model # 71A3802.

So, Frank is right if he is using the lag type ballast without the capacitor to drive the 250W Iwasaki Lamp. What this means is that he is using the low power factor circuit, and possibly paying more for the electricity bill. Now if he were to use a capacitor it should on the input lines, and that will make that into a High Power factor circuit.

Whether, this makes the lamps put out more light is something I have not tested. I have been using the dual H33 and M59 ballasts to drive my Iwasaki lamps. The lamps work with these CWA ballasts too, but are not the recommended ballasts by Iwasaki.

What I am unclear of at this point is whether, the same core and coil and capacitors are used in these different circuits, or these are different. This needs some more research.

The Iwasaki lamps work with the dual MV and MH ballasts, and I have not tested the difference in power comsumption and light output. The big advantage with using the dual MV/MH ballasts is the fact that, I can use the same ballast to drive the german 10KK if I want to, without switching ballasts. Now if I were to switch to a MV only ballast to drive the Iwasaki lamp, I may have to change ballasts if I switch to any other MH lamp.

I hope this explains why, Frank's lamp still work fine, even if he does not use a capacitor.

Unfortunately, I don't have all the answers. The deeper I got into lighting the more I realized how little I know...