Is light leakage a concern from day one?

Is light leakage a big concern from the day that the seedling breaks ground? Or is the subject increasingly important as the plant matures?

I don't imagine it makes any difference if they're feminized seeds or regular seeds but fem is what we've got.

It becomes more of an issue during FLOWER when 12 hours of darkness is needed.
A flash of light confuses the flowering plants.

I go so far as to have a green coloured bulb in the lightshade - so mistakes are easier to avoid.

north is right. more sensitive in flower, more so for femmed beans.

Not an issue at all during veg. Some run a 24/0 veg cycle.

Plants will vege just fine with a light leak but you will have a load of problems when you come to flower those girls. Once in 12/12 they require uninterupted darkness or you will have (in decending order of issue): a longer flower period, lower yield, possible hermies, no buds forming at all.
Really all light leaks should be addressed, if light is coming in then light will also be coming out and after nightfall is a good way to get busted.

What about when plants are outside. Does the moon light mess with them??

The moon creates light so what's the problem if lil bit of light gets threw

When growing inside light leaks are not desirable when flowering. Plants growing outside do get light from the moon however it's different. Just make sure you have total darkness wheny ou switch to12/12 for flowering. I've been growing indoors for over 3 years and only from feminized seeeds. No light leaks because I grow in a tent and I've never had a problem. Alwaysproduce excellent smoke in decent quanities. If your worried about having light leaks you may want to try autoflowers.When I grow those my lights are on 24/7. They aren't effected by light leaks.

I've read a couple of articles that asked the same question about moonlight. I'm not sure anybody knows why, but apparently if you're doing it inside you cannot afford to be the least bit cavalier about this. You have to engineer total darkness.

Any light leak below 2000 lumens isn't going to effect your plants flower cycle.
So, if the light leak looks to bright; it is.
If it looks less than moon light, honestly, I wouldn't worry about it.
You're not going to find any hard evidence of negative effects for light leaks under 2000 lumens.

^^^i've never checked the lumens, but i've had light leaks 2 times, and gotten nanners both times. never again, not worth the risk.^^^

Hi: all
Well l have interrupted my dark time a few times in the last few weeks and no problems what so ever and not the last time neither perfectly mature buds in time for tea and all the girls were fem seeds from Nirvana.
l think with a combation of over feeding and light leaks increases the level of stress on the plants and its way to common for growers to over feed(force feed)there girls l use a rule in soil growing max. 900ec feeding once a week and this time lm growing in coco so max. 650ec feed/water every 2nd/3rd day and has steered me right so far and the last year or so . BUT to everyone yes avoid light leaks. To have none is the key but l never had trouble from taking a pic here and there or double checking in on me girls now and again.
Peace