To be most effective, the pad(s) in your system should cover the entire area where pain relief and increased circulation are needed. The largest pads, such as the Large 264 Pad in HealthLight’s Clinical Line, would be the most helpful to treat upper or lower back, hip, shoulder, or knee pain; while small rectangular-sized pads such as HealthLight’s Small 90 Pad would be helpful to relieve pain in the neck, TMJ area, or wrist. HealthLight’s 132 Medium Pad is helpful for joint pain in the hands and elbows but is still is big enough to tackle hip, back or shoulder pain. That explains why it is a popular choice. Long thin pads such as HealthLight’s 180 Pad can be wrapped around joints, placed on the sole of the foot and is handy on the spine and neck. The Focus 64 Pad had many NIR diodes and can be used to more intensely treat localized small areas. For leg and foot issues, the 122 Foot & Ankle Boot and the 131 Foot & Calf Boot are available as either a single or dual boot system.
The Large 264 pad makes short work of back pain.
Another factor is wavelength, or the color of the of the diodes. For most uses, red and NIR (near-infrared) is the best choice for maximum penetration. When issues are on the surface of the skin, blue may be a great choice since it deposits most of it's photons in the skin. And if you like the idea of both blue, red, and infrared, the Tricolor 180 pad will be a great choice.
The Long 180 pad is great on the knee but can wrap many other joints.