I doubt you'd want to try on your grow, nor would I. I beg to differ, but it DOES matter.
A brief, flash in the pan type of interruption most likely won't make a diff. I forgot my cigs in the room one evening, and used my phone as a light to get 'em. I doubt the plants even saw that light.
BUT....a constantly on dim red power light (just like the ones on my timers) WILL affect them. I know from first hand experience that you can read a newspaper by moonlight in nature. (and in a lot of more rural areas), and lightning strikes can be blinding, both of which occur in nature, but I am here to tell you that the constantly on little lights you wouldn't even think about can cause you problems. Bright as hell instant (or mostly so) flashes won't hurt, but do that enough and it will. Most newbies (myself especially) have a need to see & check up on the plants that borders on mania. Your wife (or girlfriend, husband, I don't care) brings home a fern, and it's no big deal. Introduce a pot plant to that equation.
Best thing is to reinforce the unholy horrors that will happen should they violate the sanctity of the dark.
They'll figure it out eventually, but by then they'll most likely be over the "newbie" syndrome, and won't be forced to look in on them every 10 min.
Go telling them that it's OK within reason, and they're screwed. "within reason" to you and I is most probably alot less than it would be to a newbie. "Lets take just one more look, what can it hurt?"
