SoLux bulbs are generally recognised as the best bulbs in the world for colour reproduction. They will provide a much better and more accurate print viewing environment than regular halogen downlights.
SoLux bulbs are special halogen downlight type bulbs with an MR16 (AKA Gu5.3) fitting, so if you have existing halogen downlight fittings in your room, it is simply a matter of replacing your existing globes with SoLux globes.
In Australia, this fitting is generally only found in ceiling fittings, or track lighting, and NOT in lamps. Please check your light fittings for compatibility with both the fitting and your chosen wattage before purchasing bulbs.
Once you are sure you have a suitable fitting for the bulbs, the choice comes down to 50 watt versus 35 watt, normal bulbs versus the black backed bulbs, and the colour temperature.
If you are using your lights at ceiling height, you will want the 50W globes. If you are using track lighting or have managed to find a suitable lamp, then you will most likely want to use the 35W bulbs as the 50W bulbs will be too bright.
The black backed bulbs are definitely more expensive, but they are also definitely the most accurate. The black backing blocks unfiltered light from leaving the bulb through the back of the lamp. This unfiltered light can bounce of your fitting and come back out the front of the fixture, and will have a warmer colour temperature. This will mean your regular bulb will, in practice, usually have a slightly lower colour temperature than stated, but it does depend greatly on your fixture.
If you want the most accurate light, go for the black backed bulbs. Given then bulbs last several thousand hours in normal use, the extra expense over time in minimal for the accuracy gained.
Almost everyone should buy the 4700K bulbs as these give the best colour
accuracy and match to the D50 print viewing standard and to natural
daylight. Some people prefer a warmer light for gallery display,
particularly black and white photographers, so 3500K may be suitable in
those situations. This temperature is popular in European galleries, but
in general, Australians prefer cooler lighting - probably because of
our hot climate.