When setting up your print viewing area, you may want to measure the light that is emitting from your SoLux bulbs to check it is at a correct level. This isn't as straight forward as it may seem, as light mix measurement is quite complex. Most regular transformers are in fact not very good at outputting precisely 12 volts (varying between 11 and 13V), which causes some change in colour temperature. We recommend a high quality electronically regulated 12V transformer is used if possible.
Other factors may affect your Kelvin light reading as well, like the colour of your walls, any light escaping from the back of the bulb and being reflected by your fitting (black backed bulbs are designed to solve this issue and thus tend to be more accurate), the colour of your shirt, etc.
In our own testing, SoLux bulbs emit light around +- 300K from their stated light temperature when driven at precisely 12V and measured at the lamp itself.
Even if you measure a somewhat different Kelvin temperature, the CRI (Colour Rendering Index) and overall spectral output of these globes remains unmatched by any other affordable lighting option and are an excellent match to D50/daylight without weird spectral spikes like fluorescents have.
If you're interested, there's a very good PDF on this here: Babel Colour Light Testing.