system
Given the following post, respond as if you're commenting on Reddit:
human
[SG1] Can a Goa'uld maintain full control of the glowing eyes and deep voice or is it involuntary?

It seems there are two main times when a Goa'uld will do the glowing eyes and deep voice thing -

1 - To willingly show off they're a Goa'uld or intimidate.

2 - When they appear to lose control of their emotions such as times of anger and rage.

Is this an involuntary action they can't control?

Can they glow their eyes for longer periods of time say to function as a torch in a pinch?
gpt
One instance comes to mind that might throw a third possibility into the mix. During apohis's first attempted invasion of Earth, a recently awoken Klorel was fired upon with missiles. All he had to do to defend himself was raise the shields, a simple task. However, his host Skaara was apparently resisting quite valiantly, and his hand stopped short of the controls. It wasn't until Klorel's eyes glowed that he regained control.

I personally expect that the glowing eyes are not just for show, but actually signal a realise of hormones or chemicals which increase the symbiote's control of the host. This is why it is often seen right before they do something really cruel, or immediately after taking over a new host.

This is also why you never see a Tokra use the glowing eyes.