Saidar (pronounced: sah-ih-DAHR) is the female half of the One Power. Unlike the more violent saidin, saidar is said to be a "river of Power" which must be surrendered to or "embraced" in order to gain control.
Female channelers can tell when other women are touching the Source; a white glowing aura appears around their body, only visible to those trained to touch saidar. The ability can also be sensed in any woman capable of channeling, be they wilders or Aes Sedai. In the testing to see if you can channel, a woman channels a simple weave and waits. Within five minutes if a woman has the spark, the woman tries to channel the flow, and the test is confirmed. It takes longer for those who only can learn. However, a woman who has the spark can be detected by another female channeler without being tested.
Saidar is described as gentle, but infinitely powerful; a force which will do what you wish it to, but requires patience and submission to properly channel it. Surrender is necessary to gain it, and women universally speak of it as "embracing" the Power. Weaving for a female channeller is described as "guiding" the Power to perform the desired task. By contrast saidin is often described as a "raging torrent" that must be "seized" and controlled in order to force it to submit. Because of this fundamental difference in channeling the Power, a man can never teach a woman to channel, and vice versa.
There is almost no way for a woman to tell when a man is channeling, though the residues of his channeling can be detected using an appropriate weave. Lanfear shows the ability to sense male channeling up to the extent of knowing where the weaves go when fighting with Rand al'Thor by means remaining unknown. Recently an active method was discovered to discern whether or not a man was channeling or holding saidin, but this is not widely known.
A woman repeatedly channeling saidar over a longer time starts to "slow," meaning that she does not age in the same way as a woman without the ability. This also gives the woman a longer life and some have been known to live over four hundred years.
An exception from slowing are the Aes Sedai, who bind themselves using the Oath Rod, which gives them an ageless face instead of slowing the aging. The Oath Rod is also suspected to shorten an Aes Sedai's life by hundreds of years, though after being stilled, the former Aes Sedai returns to the same young appearance as she would have if she never had taken the oaths.
Another blessing received by channeling saidar is that a pregnant woman will not be sick due to her pregnancy. However, her ability to channel will be harder to control over time and the woman will feel as if her weavings are slippery and oily – fading away as she tries to make a weave.
Groups that channel saidar
- Aes Sedai
- Some Aiel Wise Ones
- The Kin
- Sea Folk Windfinders
- Seanchan damane
- The Sharan Ayyad
- Female Forsaken
Saidar Strength Ranking
Initially Robert Jordan said that he knows the relative strength of every female channeller in the books imposed on a 21 level scale.
I have said that in my notes I have such a scale that I use to keep track of everyone, but its main use is for the lesser characters, in particular Aes Sedai, so that I can check on who should defer to whom, who should only listen a little more attentively to whom, and so forth.
Later this scale was expanded two times. The first was a new scale of levels between 1 and 60. Later again he added 12 levels above the former 60 levels scale. In his notes Jordan explained that on the 60 level scale the Aes Sedai were comprised between level 1 (the level of Elaida, Romanda Lelaine, Moiraine, Siuan, the strongest living Aes Sedai at that moment, because Cadsuane was believed dead) and 33 (that of Daigian, the weakest living Aes Sedai); between 33 and 60 were comprised the female channellers too weak to be tested for the shawl. The arriving in the Tower of Nynaeve, Elayne, Egwene, and the return of Cadsuane needed a scale to classify better the stronger channellers above the level 1. So the 60 levels became 72, and the former level 1 became the level 13(1). The new first level, the level of Lanfear, was indicate as 1(+12). For instance that of Cyndane 2(+11), Nynaeve 3(+10), Moghedien 4(+9), Elayne 8(+5), Nicola 9(+4), Meilyn 11(+2). This is the classification that we can find in the "The Wheel of Time Companion".
But the levels of strength given by "The Wheel of Time Companion" have to be taken very cautiously. In too many cases they are completely in contradiction to the descriptions of strength that we can find in the main WoT books. For instance the positions of Cadsuane, Aviendha, Graendal, Semirhage, Mesaana, Viendre, Kwamesa, and others are totally wrong; also too many Sitters in the Hall are classified in low levels, among Aes Sedai described in the books having an average strength.
Saidar Strenght Ranking Table (this is the first 21 table used by the author that later was expanded to a scale of 60 level and again to one with 72 levels, but the last one is with some contradictions and in need of clarification. In bold it is signed the position of every channeler that we are sure about their strength when compared to others or we have a very good approximation).
- The Eye of the World, Chapter 12
- Knife of Dreams, Chapter 23
- Robert Jordan on his blog
- based mainly to 
- The strongest, maximum level known since the Breaking
- "Alivia is...considerably stronger than Nynaeve"
- After her reincarnation in Cyndane, Lanfear was a little weaker than before, but still stronger than Graendal
- "The girl was stronger in the One Power than she herself! Even in her own age that had been uncommon among men and very rare indeed among women" Graendal on Cyndane (TPoD Ch. 12)
- Graendal is second in the One Power only to Lanfear and few were able to match her
- Nynaeve is defined the strongest Aes Sedai since the founding of the Tower
- She credits herself with never having met a woman who is stronger. That was, until she met Graendal
- "Talaan matched her as closely as made no difference...the light alone knew what her potential was"- Nynaeve's PoV (WH, Ch. 10)
- Minimum level for female Forsaken
- Ranked among the strongest Aes Sedai since Cadsuane, just a level below the Forsaken
- Cadsuane was the strongest Aes Sedai in a Millennium until the arrive of Nynaeve, Egwene and Elayne
- Bode and Nicola have a potential strength described as not far to that of Egwene
- Aes Sedai on this level, or more, are considered very strong
- Minimum to use the Choedan Kal safely. In the last twenty years Aes Sedai on this level were on the top of the White Tower hierarchy
- The sisters on this level are considered very influential Aes Sedai
- Aes Sedai on this level (or more) are defined strong; minimum to become Amyrlin Seat, that usually are chosen among the strongest Aes Sedai
- Minimum to be an influential Aes Sedai; minimum also to become Sitter, Ajah Head, Keeper of the Chronicles, Mistress of Novices
- they were "Chosen from the strongest of the Shaido Wise Ones who could wield the One Power" along Therava and Someryn
- Quite Strong Aes Sedai. Minimum for opening alone a suitable gateway to travel
- Crossroads of Twilight Chapter 12
- Just a level above average Aes Sedai
- Medium level of strength, average Aes Sedai
- Not very strong, but linked in a circle of two elements they are able to open a small gateway, merely large enough to go trough
- The weakest Aes Sedai. They were barely strong enough to gain the shawl
- Quite weak. Barely strong enough to become an Accepted
- Weak, even not enough to become Accepted; but some of them have a strong talent in Healing or in other weaves; Sorilea has the talent to learn a weave after seeing it only one time, like strongest channellers as Alivia
- Very weak; but linked in a circle of four they are able to open a suitable gateway
- Minimum known, barely able to touch the source and to form a weave