Light Reflection

This is somewhat a science question and a horticulture question rolled up in one. I have a 2x4x7 Mylar grow tent. This tent supposedly reflects 95% of light. Now it seams like this would have a huge effect on how much usable light my plants receive but I just posted a similar thread (I guess it wasn't specific enough) and had people tell me that the quality of the light reflected off Mylar is not very useful for the plants. This is throwing my physics understanding out the window. Please explain why reflected light is not very useful or if some idiot just gave me bad advice? (beyond the fact that 5% of (photons or energy?) is lost each time light is reflected

reflected light has minimal lumens or pentration. but not a concern. it is what it is and use it. its not bad light just not as the bulb outputs. its better than having a black wall....lol

what do people mean by penetration? is it just that after a certain distance the light is to diffuse to do a good job or is it that certain wavelengths only travel so far before they are absorbed by the air?

also keep in mind that not all substances reflect the same spectrum. Regardless, my understanding of how mylar was developed was to be used by NASA in horticulture experiments in space. Discounting the possibility that it was designed to suppress certain spectrum that isn't being filtered by the atmosphere, I would imagine it is going to be the best reflector for horticulture for the price. If you really want proper reflectivity, you want what's called polished spectral aluminum. That's what the high quality light reflectors are made of.

Dako said:

what do people mean by penetration? is it just that after a certain distance the light is to diffuse to do a good job or is it that certain wavelengths only travel so far before they are absorbed by the air?

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the intensity of the light (think watts per area, so a flo tube is spreading that watts over X inches, and an HID is generating light from an area of say a few mm) determines how deep it penetrates. Think of a flashlight, does the light get focused more to a point which illuminates further, or diffused over a greater immediate area which doesn't extend as far. HID's can actually illuminate leaves through other leaves, due to their penetration, you'd be hard pressed to do that with a florescent without burning the plant.

Has anyone actually placed a light meter say 3 feet from a hid in open space and then done the same thing in a 2x2(or any small) Mylar tent? Just curious
based on what you all know about the light plants use, would this even reveal anything?

not sure what good testing refcetive stuff in space does with no atmosphere to effect it like we have down here.

and by pentration i mean how deep into the plants foliage the ligtht can travel at a distance. inverse square law says from a center point of light each foot away the light the candle power is only 25% the intensity or foot candles. and all relates to lumens. with hoods we do get a bit more. on average a 400 is about 18 inches of full light, 600 at 22 inches and 1k is only 2 foot. the light dimishes diff in hoods so after this initial depth each inch more is 50% the full lumens. so a 1k bulb in a hood measured at 25 inches is only now a 500 watt worth of lumens or light pentration. with the reflection its even way less. i havent measured the drop for that. and yes each reflective material we choose has a diff rate of this and what colours it obsorbs