I'm thinking about buying a fluorescent lamp to light up a 40cm X 40cm softbox. I need to take pictures with a pure white background for an online catalog of jewelry (gems, emeralds, etc). Is a 490-lumen fluorescent lamp (bulb) enough?
A single lamp is enough to achieve consistency in the white background of all the pictures? In the few tries I've done holding the light source (bulb) with my hand I have obviously obtained inconsistent white backgrounds (some areas of the background end up brighter/darker in the different pictures).
I need some advice about lamp (lamps) positioning: from what I've watched and read, it looks like a single light from above is good enough. But other sites say light from the back of the softbox is what I need for max contrast.
Does the camera angle affect in any way the background light I get in the pictures in the softbox? Is there a "optimal" angle for max background brightness?
The short answer: It doesn't matter how many lumens your light illuminating the back of your softbox is. The background just has to be lit brighter than your subject.
You need more light on the background so that you can intentionally blow it out without blowing out the product. Then expose so that the background is on the verge of blowing out. In post-processing push the exposure for the highlights up until the background is pure white.
This has been covered many times here in the past:
How do I improve the results of photos taken in a light-box?
Why hasn't buying powerful lights improved my lightbox images?
How do I properly do shadowless product photos?
Why can't I get a decent white background with product photography?
Why can't I get a pure white background, even using multiple light sources?
How can I inexpensively create the white backdrop look?
One of the best ways to force a background to record as a solid white is to use a translucent background like "milk glass" etc. You illuminate the background from behind and adjust the brightness of this lamp so that the milk glass records void of detail.