how do you trap fluorescent light in a glass greenhouse at night while still allowing sunlight in.

I have a glass greenhouse.  I use grow lights for my seedlings.  At night the light is a bother to neighbors.  Is there a way to reflect the light back into the greenhouse without significantly decreasing visible light during the day?  I can loose some UV and heat without loss of performance as I currently get a little too much of both.  I thought of using exterior rated mylar silvering films on the interior.  The interior can reach 105 (when I forget to open the window) and the humidity is often 90%.  Thanks for your help.

I’d look into the technology used for light deprivation (“light dep”) in growing “the plant not to be discussed on this forum”. You could modify the material from blackout fabric to a panda (black outside, white inside) film or something like that. Most automated systems seem to work with rollers on timers and weighted bottom edges.

How many hours of light are you providing?  I was under the impression that people only illuminate seedlings for 16 hours or so a day.

Do you need to blackout the greenhouse entirely, or just block the most direct light?

My neighbour across the street is putting in a commercial greenhouse.. I'm pretty sad to be losing my darkness. Nice of you to accommodate your neighbours concerns.

There's a name for this -  it's called "light pollution". Closer to the local observatory there are actually rules against "unnecessary outdoor lighting". Unfortunately, this type of pollution is not nearly as well researched as it should be. I admit, I've always been extremely sensitive to light at night in my bedroom, so I appreciate efforts people make to keep their lights under control.

I realize that at certain times of the year, extending the hours of light is important. I have a small set-up on a window ledge and I add light for 1 1/2 hours in the morning, and  from dusk until 10 pm, and that pretty much covers the 16 hours needed. I realize that some people prefer to light their plants in the middle of the night to get cheaper electricity, but luckily that's not an issue where I live, the lights are very efficient and since I'm normally in the same room in the evening, I also benefit. Maybe the neighbors wouldn't be as bothered if the lights were only on from 6 am to 10 pm. You could shift the time a little one way or the other if that worked better for your neighbor's schedule.

Siri Atma Khalsa, if you have too much UV and heat, have you considered installing some of the "reflective bubble wrap" on the outside of parts of the green house that aren't providing useful natural light? (it's like this: https://www.homedepot.ca/en/home/p.48-inch-x-25-ft-double-reflective-insulation.1000167795.html) Many greenhouses have more glass than the plants actually need based on the climate and the greenhouse might be more efficient if some sections were blocked. This is why if I had a greenhouse, I would actually insulate the north and west walls, and the north part of the east wall. I'd need more glass area in my cloudy region than people with more consistent sun, but conserving the warmth is equally important.

siri atma khalsa wrote:I have a glass greenhouse.  I use grow lights for my seedlings.  At night the light is a bother to neighbors.  Is there a way to reflect the light back into the greenhouse without significantly decreasing visible light during the day?  I can loose some UV and heat without loss of performance as I currently get a little too much of both.  I thought of using exterior rated mylar silvering films on the interior.  The interior can reach 105 (when I forget to open the window) and the humidity is often 90%.  Thanks for your help.

Ben gave you the answer. If you inquire with your local 'hydro' or 'grow' stores you should be able to find some options. Up here part of the rules for the permitted cannabis farms is that they have to abide by some international light pollution standard, their solution is to cover the greenhouse after dark if they have lights on. you could probably rig up a smaller frame insed the greenhouse to just cover the plants/lights that would take you 5 minutes to put on/off each day.

I am currently using a timer that gives 18 hours light.  I am turning off 10 pm to 4 am.  I can't stop the light from exiting the roof, which is lexan, and isn't very bright, the side light in the 24 to 30" the lights are suspended above the seedlings goes out by my pool and then reflects up several trees.  I am certainly concerned about causing light pollution to my neighbor's yard and wasting the light.  I am growing ornamental datura seedlings that respond to intensity and length of light.  These seedlings also get very weak if they are leggy.  The extra light also seems to help my brugmansia cuttings, which supposedly respond more to heat, but certainly don't seem to mind some extra light.  Both of these are part of my program to slow the gopher activity down in my food forest.  I am growing plants that are toxic to gophers, but have economic value, in between my fruits.  I have significant problems with gophers destroying my figs, dragon fruit, and artichokes.  I make some rather sophisticated gopher bags and I trap what I can, but I am one acre next to 17.5 acres of wild, gopher infested land.  Even herons come by to hunt gophers.  I have catnip mint to attract cats.  I think the crows have become so invasive they are keeping the raptors at bay.  When most of the crows migrate south in the fall, I see the raptors show up again.  I keep piles of rock to attract reptiles and plant plant shelters to allow the reptiles to move form rock shelter to rock shelter.  I have thought of barn owl boxes, but I am close to a road, so I am not sure I have the privacy for them.  

There are machines that draw a shade cover on a timer. If the light comes on when there is still some daylight, and the cover follows shortly after. It would retract the cover after the light turns off, ready for a new day. these are about the size of a small fishing shanty.