Hey realms, i've got a question about this card. After the activation of this card, does the opponent have to play his/her monsters face down until the effect ends on the second standby?

No.

SOCL only affects the existing monsters on your opponents side of the field at the time of activation. Monsters your opponent summons after that can be summoned in face up attack.

I thought so, hey thanks for the insight

It's also pretty clear on the card itself

Swords of Concealing Light
Continuous Magic
When you activate this card, change all monsters on your opponent's side of the field to face-down Defense Position. While this card is face-up on the field, monsters on your opponent's side of the field cannot change their battle positions, except with a card effect. Destroy this card during your 2nd Standby Phase after activation.

Nowhere on the card does it state "While this card is face-up on the field, when your opponent plays a monster, it is Set in face-down Defense Position"

and once again you score another point Half lol, common sense makes the most sense lol but yeah your right though, I had to think about it a little bit before I read this

While it doesnt cause monsters that are summoned after its resolution to be placed face-down, it is a Continuous Effect which is similar to Gravity Axe - Grarl. The monsters cannot change their Battle Positions until the Spell Card is removed from the field, unless they are changed by an effect.

Well, it only applies to manual Position changing. Card effects can still be used to have positions changed.

Yeah.... I think I touched on that, but I guess it can always be punctuated....