Heidi Swapp Lightbox Alphabet Inserts - White Bold on Clear The perfect addition to the Heidi Swapp Battery Operated Lightbox (sold separately). This 3 1/2 x 3 3/8 x 1 1/4 inch package contains fifty lightbox inserts. WARNING: This product contains chemicals known to the State of California to cause cancer, birth defects or other reproductive harm. Do not mouth or chew. Imported.