The Power Screen, also known as 'Energy Shield', was originally meant to be available to the player in Quake II as a power-up, but was cut from the original game before its release (although it can be obtained by "cheating" with console commands). It is still present in the original game equipped by the Brains (including the Beta Class Brains) and the Daedalus from Ground Zero.
- Brains: 300 health plus 100 cells for its power screen
- Daedalus: 450 health plus 100 cells for its power screen
The Power Screen is powered by cells, and the general principle behind it is to absorb some of the damage suffered from incoming attacks, consuming some of the cells in return for losing less health. It should not be confused with the Power Shield, although they have some similarities - the Power Screen is essentially a less effective version of the Power Shield. It has a lower absorption rate than the Power Shield, and it only protects its user against damage to the user's front, whereas the Power Shield protects against incoming damage from all directions. The omnidirectional protection of the Power Shield also means it is effective against most other sources of damage such as slime and lava, whereas the Power Shield would only help if the damage comes from a frontal direction.
In effect, when the bearer of the Power Screen suffers damage (from a frontal direction), one-third of that damage is absorbed by the bearer's cells instead of their health, and the remaining two-thirds are suffered by the bearer's health. So, for example, a Railgun would normally deal 125 damage per hit, but against a Daedalus its power screen's cells absorb 41-42 of that damage, the other 82-83 damage suffered by the Daedalus' health
The 2023 remaster of Quake II has modified the Power Screen to make it more susceptible to energy weapons, these weapons depleting twice as many cells as non-energy weapons (energy weapons are those which use cells for ammunition, as well as the Blaster and the Phalanx Particle Cannon) So, for example, a Plasma Beam normally deals 15 damage per hit, but against a Brains or Daedalus it will deal 10 damage to its health and deplete 10 cells from its power screen.
In the Call of the Machine expansion, certain Tanks, Tank Commanders and Medic Commanders are equipped with a Power Screen even though they do not normally have them. On one level, Brains are encountered without their usual Power Screen.