Mirrors waste energy by absorbing only a small fraction of the light that falls on them.
When light, which, like radio waves, is a form of electromagnetic radiation, strikes a metallic mirror the electrons in the metal move just as they do when a radio signal strikes an antenna. Pushing electrons around takes energy, which dims the reflected image.
Metallic mirrors reflect infrared light (heat) and if your mirror has imperfections this will cause hot spots, which can burn plants. Please notehot spots also apply to Mylar and Foil and IMO is not applicable to growers using small amounts of fluorescent lighting.
By using a mirror to reflect your light on a wall, you can test for imperfections, if you see an uneven image, with focused beams (normally located at the edge of the reflected pattern) these are known as hot spots and depending on the wattage of your bulb, may burn your foliage.
Metallic mirrors should not be used as a reflector for your grow room as minimizing light loss is important.
Soooooooooooooo are they good? I have a mirror on the side of the window somtimes to try and catch the reflection on some of my plants as the sun moves thru the day is that pointless? I was wondering how much power was lost off 1 reflection if any? Thats why this thread caught my eye, but this thread doesnt really have a complete answer and why
I always thought it was the glass of the mirror which lowered % slightly as the light has to pass thru it and then back out thru it again as the light is reflected
The hot spots were from old style flat mirror Mylar that has creases wrinkles in it from being poorly instaled
They then brought out diamond silver Mylar to avoid that ( worry of hot spots )
This is all old chat we would talk about 15-20 years ago lol
There’s also the matter of just making it a pleasing environment for you as the grower my eyeballs would go bonkers in a fully-lit fully-mirrored space. Diffused silver tent walls are okay, but I’d love to get a couple white interior grow tents
Mirrors do make good reflection of light , but I don’t believe for growing it would be helpful. I remember reading a story about Thomas Edison when he was a child, his mother needed an operation. They would not operate at night because they didn’t have enough light . She may have died if they waited so what he figured out was to take the mirrors in the house and all the lamps and candles put them in front of the mirrors and reflected the light on the table and they were able to perform the surgery on his mother that being said
I had occasion to use such a thing when hurricane Sandy took out the lovely state of New Jersey and we had no electric for 10 days. I had solar lamps in my yard, and I put some mirrors up in the room and reflected the light from the solar lamps and it really brightened up the whole room
You can also point a camera at The high noon sun for s few hours, then get a 55" flat screen tv, hang it above the plants, then playback The video on s loop.
“The Italian Town That Built Its Own Sun reflected light is, of course, not as powerful as direct sunlight, but it’s enough to warm up the main square and give the town’s homes some natural sunlight. The mirror is only put to use in winter and stays covered for the rest of the year.”
my eyeballs would go bonkers in a fully-lit fully-mirrored space. Diffused silver tent walls are okay, but I’d love to get a couple white interior grow tents 
