polly tunnels blok lite?

dont polly tunnels n buble rap blok lite to ur plants?
on that note... i hav spare frosted glass from faulty double glazin units cud i use this to replace damaged panes in my green house without affecting the light intensity/ plant growth

 

Anything that isn't 100% transparent will reduce light and have an impact on growth. Polytunnels do reduce light slightly, but it isn't a major problem otherwise thousands of commercial and amateur growers wouldn't be using them. Bubblewrap also reduces light but most growers use it to provide extra insulation in winter and spring and remove it during summer. It can also be used to cover soil to get it heated up faster in spring.
Your frosted glass will reduce light but if you are only replacing a few panes I'd be tempted to use it as it may help prevent the greenhouse becoming too hot.

 

This is a quote from those that know - the growers of Marijuana indoors. :D

The type of lighting used depends "on the size of room and the type of growing method. Indoor growing requires the light intensity, ideally, to be between 2000 and 3000 lumens/sq. ft."

What Dave W says is right. As full daylight outside can be as much as 10,000 or 15,000 lumens/sq ft in summer - there is plenty of light to spare. Where the problem becomes more noticeable is in winter when light levels are low outside. But then you probably need the heat more than the light. On this scale a brightly lit office is about 500 lumens.

The full referance is here http://www.skunked.co.uk/articles/growing-marijuana-03.htm

And no I don't :D . But I became interested when I made a light box for use in winter to grow plants.

 

humulus,using bubble wrap in the greenhouse does`nt just act as insulation during the winter it also acts as shading during the summer. David.