The tension required to bring a string up to pitch varies between string materials and string designs.  I’m not going to dive into the theory of why you might want “lighter” tension strings or “heavier” tension strings, but I did want discuss how manufacturers list the specifications.  Most strings that are offered on the market are offered in light, medium, and strong tensions.  Each manufacturer calls these three tensions different things based on language and tradition.  I’m currently experimenting with Thomastik Dominant cello strings on my instrument because they are significantly “lighter” (even in the same tension) than what I was using before.  For example, a Thomastik tungsten-wound Spirocore C-string is rated at nearly 30 pounds whereas the Thomastik Dominant C-string is only about 23 pounds.  The decreased tension puts less downward force on the top of the cello through the bridge.  Generally speaking, this produces less volume but a warmer, more overtone-rich sound.  I’ll keep you posted with the results of my current experiment!