If it's time to replace conventional fluorescent bulbs, consider switching to these new high-performance bulbs. They produce a brilliant, full-spectrum light that duplicates an amazing 94% of the solar spectrum. T-12 bulbs also have a longer life than incandescents ??? up to 20,000 hours ??? and use 20% less electricity. Suitable for traditional fluorescent T-12 fixtures only. Plants get the best light and intensity for naturally healthy growth Bulbs burn for about 20,000 hours For use with T-12 fluorescent fixtures only T-12s are 1.5" diameter Produce 94% of the solar spectrum for healthy plants Up to 20,000 hours of light