Strong evidence

Light and heavy loads build similar amounts of muscle when sets are taken close to failure.

In practice

You don't need heavy weight to grow. Sets of 20 with something light build muscle much like sets of 6 with something heavy, provided you push both near your limit. That matters most when your equipment is limited or a joint won't tolerate load.

What it doesn't say

The equivalence holds for muscle size, not for strength — and light sets have to be genuinely hard, which most people find far less pleasant than lifting heavy.

Source

• Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW (2017). Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis. Journal of Strength and Conditioning Research, 31(12):3508–3523. doi.org/10.1519/JSC.0000000000002200