When growing indoors, light intensity and spectrum become even more important. The quantity and quality of light are the most critical factors associated with successful plant growth. Regular lamp replacement is essential.

Lamp Type Optimal Growth Average Growth Maintenance Growth
HPS 9-10 months 11-12 months 13-16 months
Metal Halide 6-8 months 9-10 months 10-12 months
e-Start Metal Halide 9-10 months 10-11 months 11-12 months