How to Make Your Own North Light
I remember many years ago I watched a video of David Leffel's painting still life. A student was asking what kind of light he uses for illumination. David said he uses the natural north light. "If you do not have a north or east window in you studio, you might have to move" David put it in a humorous way to address the importance of the proper illumination.
Well, my north window doesn't help, because I only have time at night to paint. I have to rely on artificial lights for my paintings. I started with conventional tungsten light and did some paintings. They look pretty good under the light. However, at the next morning, I looked at my work under natural daylight. My painting has completely changed. The colors are way off. So I learned my lesson.
I tried many different bulbs and finally fine the best solution: using color correcting light filters. They are blue tinted transparencies and very easy to use. You simply clip the filter on the reflector of your lamp, Voila! You have created your own north light. If you think your light still too yellow, you can double the filtering. You might have to use a brighter light of course.
You may ask why I don't use fluorescent light to get a cooler light. The major drop back is that the fluorescent light does not have a continuous spectrum light like the sun, tungsten and halogen lights. It would not give the color accuracy of the pigment, especially high chroma colors. The spectrum of a fluorescent light is discrete dominated by the mercury spectrum, which only have four lines.
The filter has a strong heat damage threshold, so it is absolutely safe to use with tungsten or halogen lights. To prevent the bulb overheating, please leave an air gap around the reflector.