The Hubble and James Webb telescopes use reflective telescopes. Each telescope uses a series of curved mirrors to bend the light and send it to the proper collection instruments.
The James Webb telescope’s primary mirror is 21.3 feet in length. The Hubble’s primary mirror is 7.9 feet in length. The difference in size gives the James Webb telescope the ability to collect light from an area that’s six times larger than the Hubble.
The James Webb can collect more dim, redshifted light than the Hubble. The James Webb will be able to collect data from objects that are 100 times fainter than what the Hubble can detect.