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Use a 20-watt compact fluorescent bulb (or even brighter if your shadow box is large) for your still-life shadow box light.
If you purchase multiple bulbs of different wattage it will allow you to adjust the brightness of your still-life light by switching bulbs — compact fluorescents are not dimmable. Although I have seen some dimmable versions for sale, I was advised against using them as they do not last.
The very best option (although more expensive) for a shadow box light, would be a very bright, dimmable LED light. An LED bulb on a dimmer switch will make it super easy for you to balance your whites. If you do use a dimmer switch be SURE to lock down (with masking tape or something) the dimmer switch AFTER you have balanced your whites. Refer to this video for how to balance your whites: youtu.be/TuZ0t5FR9f0
Do not use incandescent bulbs at all (the old-style regular light bulbs), either for your shadow box light or your studio light. You simply will not be able to judge your colors accurately if you use them. For instance, you might think you are painting with brown paint, but take the paint outside and you will see that it is a dirty purple.
If you live near a large city, you can find 5000K or 5500K bulbs at a light bulb specialty store. Try looking them up in the phone book. If you can't find one that sells them, try searching Google with the words "5000K fluorescent" or "5500K fluorescent" in the search field.
You can use carboard for that too assuming you use a low wattage/low heat out-put. LED dimmable is best. You have to get inventive with how you can adjust your light to make the shadows where you want them. If you have a support for the light it doesn't really have to be in a tube or box. The tube/box is to keep the extra light from spilling to where you don't want it. at one one time I had clip light clamped to a chair next to the shador box shining through a narrow slot. Then I had to put an extra piece of carboard taped to the box to shade me from the light. No rules, no need for engineers just "enginuity".