White screen vs. physical lightbox
A physical A4 lightbox costs $30-50 and only produces one fixed brightness. Your tablet or laptop already has a high-brightness display with variable output — using it as a lightbox saves money and gives you adjustable illumination for different paper weights. The only tradeoff is you can't press hard on the screen, so use a light touch.
For standard copy paper (80gsm) set brightness to 100%.
For standard copy paper (80gsm) set brightness to 100%. For tracing paper under 50gsm, 70-80% brightness is plenty. For heavier illustration paper (120gsm+), maximum brightness may still be marginal — thin the source image by increasing contrast before printing, or switch to a physical lightbox for consistently dense output. iPads and high-end laptops generally have brighter displays than budget tablets.
Tracing applications on a screen lightbox
Calligraphers use screen lightboxes to trace practice sheets, embroidery designers to transfer pattern outlines, tattoo artists to draft stencil flash, and digital illustrators to convert hand sketches into vector work by tracing scans. The flat glass surface also makes it easier to slide paper around than a bulky physical lightbox, which helps for long-form projects.