Of course, using an HO or VHO ballast will be a faster printing method, but at the substantial expense of the lamp life. Using these ballasts with normal output lamps is not recommended, and may not be electrically safe due to the much higher amperage that the lamps are operating at.

If you look at the ends of the lamps, you will probably see what's known as end-wall blackening. This is a result of the cathodes in the lamps sputtering off the tungsten that makes up the cathodes. This will occur much more rapidly with an improperly driven lamp, and will eventually cause the lamp failure.

Additionally, the extra heat that is generated by overdriving the lamps will bake the phosphers, and reduce the efficiency of the lamp more rapidly, so you had better have a very good way to remove the heat generated by the lamps.

Personally, if you want to use a HO or VHO ballast, be my guest, but it's not something I would do. Besides, if you are concerned about cost, then using an HO or VHO ballast is definately not going to be on your solution sheet, as they tend to be very expensive compared to normal output ballasts.

If you get normal output ballasts, it may be possible to find three or four lamp electronic ballasts, which will reduce the number you have to buy. If you use HO or VHO, you probably won't find electronic ballasts, so you will need one ballast for every two lamps. Combine this with the higher cost per ballast, and you suddenly get a much more expensive setup, that is much less energy efficient, and will burn up the lamps more quickly.

I do recommend electronic ballasts, even though they cost more. Make sure you get the appropriate ballast for the lamp. Some of the BL lamps are T-12 lamps, and most electronic ballasts are for T-8, so be sure that you are getting the appropriate ones. Also, make sure that all the ballasts are of the exact same manufacture. This is important because the actual output from ballasts can vary by manufacturer, and you can get differences of as much as 10-15% in lamp output depending on the operating characteristics of the ballast. That can cause uneveness on the image under certain circumstances.

BLB lamps are essentially BL lamps with an added Wood's filter applied to the glass before the phosphers are coated onto the glass. There is no possible way that they will ever be as efficient as a BL lamp, although the difference may be slight. If they are readily available at a reasonable cost, then I suppose it may be a reasonably alternative, but you have to be more careful around these lights.

The BLB lamps don't have the majority of the visible spectrum that the BL lamps contain. This will result in a relatively 'dark' appearence to the light, which is useful if you have a bunch of phychedelic posters or whatever, but this also means that your pupils will be dialated with this light source, which can result in your eyes receiving much more UV light than with the BL (or other) lamps.

While this isn't an issue if you do this a few minutes a week, if you spend a lot of time around the lamps, you might want to be more careful about eye protection. Most home centers have good safety glasses that will eliminate a very high percentage of UV. They should be used if you are going to be around any of these light sources a lot, but it is much more important around the BLB lamps.

In most cases, the 2' BL or BLB lamps have about 10,000 hour life expectancy, and the 4' lamps have about 20,000 hour life expectancy, and the 4' lamps are often priced cheaper than the 2' equivalents, due to volume issues. I would recommend making a 4' unit. It will allow you to print on multiple negatives at any one time, or on larger neagtives without difficulty, and there is almost no drawback to the larger lamps, other than the larger unit, which reduces portability, and the increased energy usage when in operation.