Blind Faith is an achievement available for iPhone, iPad, PlayStation Vita, Android, and Nook versions of Plants vs. Zombies. It requires the player to complete a super foggy level (Levels 4-7, 4-8, 4-9, and their Quick Play variants) without using Blovers or Planterns to make the fog "disappear". It is similar to the Nintendo DS achievement Nebulaphile. However, unlike Nebulaphile, Torchwoods can be used while earning it.
It is advisable to have the following:
To know whether or not a zombie is in the fog, plant a long ranged plant such as a Scaredy-shroom or a Peashooter. The player can use these two plants to sense whether or not there are zombies by attacking them from afar, but plant Puff-shrooms at the beginning of the level because there are not a lot of zombies at the start. Once the player had built his or her sun production, let it produce sun until he or she has enough sun. After that, remove the Puff-shroom and grow long ranged plants.
This achievement requires that the player must not use fog removers. A wise strategy would be to create a defensive line of Garlic backed up by Wall-nuts or Tall-nuts and Gloom-shrooms on the second and fifth lanes. Cattails are also a very preferable choice, as they can hit any zombie on the screen. This not only defends all six rows, but can also notify you of where zombies are.
Also, if you're desperate to see in the fog a little, then use Torchwood. He can get rid of some of the fog, and you will still be able to win the achievement.