Why was Bilbo's sword not glowing?

Question

In some places in The Hobbit: An Unexpected Journey, 'Sting', (Bilbo's sword) wasn't glowing blue. There are a few scenes where Bilbo is around Orcs, Even one where they were fighting the Pale Orc, but the sword was still not shown to glow.

Sting had the magical ability to detect orcs or goblins nearby. When orcs or goblins were present, it glowed blue, as it did when the Fellowship encountered orcs in the mines of Moria. This was a common property of First Age Elf blades, particularly those forged in Gondolin.
- Wikipedia

So if I'm not blind, is there some explanation for that or is it just a mistake?

Answer 1

It is a mistake

From: The Hobbit: An Unexpected Journey - the worst continuity errors

Sting!

The sword that is affectionately known as Sting has a magic property, it glows blue when enemies are near. We know that because in 'Lord of the Rings' Frodo has it, and it does indeed glow blue when enemies are near, like in the Mines of Moria. However, during the Orc attack on the cliff at the finale of the movie, Sting doesn't glow at all

Answer 2

Another possible (in universe) explanation: It only glows around Goblins, and Goblins and Orcs are different races.

There is some controversy over this however; it's somewhat of an on-going argument if Goblins are Orcs are just different names for the same creature, or are two totally difference races. (see this question or this one).

But, if the two actually are different races it would explain why the sword glows in the Goblin tunnels, but doesn't glow when fighting the Orc raiders.

Answer 3

This is pure speculation but i might be because it only glows with living orcs and goblins. I think that Azog and his hunters aren't living orcs but that they were in fact killed during the Battle of Azanulbizar. But then there is our Necromancer who can summon the spirits of the dead. So my believe is that Azog and his hunters are undead orc brought back to life by the Necromancer and that why i think Sting does not glown when they are nearby because they are not living orcs. The scene when Gollum kills that goblin and Sting stops glowing right after it is according to me a nice bridge that Peter Jackson inserted to make the bridge that Sting only glows with living orcs.