We moved the plants from our grow lights in the house to the GH two weeks ago. The night time OS temperatures have been holding between 5-20 degrees Fahrenheit since we planted so it has been too cold in the GH (29-36 degrees night time) and I have not been able to turn off the bulbs to give them darkness.

Has anyone had experience with growing Tomato plants using light bulbs to keep them warm during the night? How long can the tomato plants survive without darkness? How much dark should tomato plants have? I have not been able to find much information regarding tomatoes and darkness on the web?

In alaska, during the summer, the sun hardly sets right?

Photoperiodism
Photoperiodism refers to a response in a plant to the changing length of day and night. It helps plants to pollinate and produce flowers. "Short-day" plants require short periods of light, while "long-day" plants require longer exposure. Tomato plants are "day neutral," which means their flowering cycle is not determined by the period of light to which they are exposed.

Photosynthesis
Still, tomato plants require darkness for the process of photosynthesis. Energy collected from sunlight is converted into sugars during the night hours. These sugars serve as food for the developing fruit.

Light Requirements
Although tomato plants can be grown under artificial light in greenhouses, they do require at least six to eight hours of darkness every day to ensure optimal growth............

Having read this - experience from someone who has grown tomatoes with lights for heat during the night may have suggestions for success? It appears from the above information that seedlings (not producing fruit) may be OK without darkness - although growth may be a consideration?

Hope this helps somewhat.

The tomato plants are growing - this is how they looked today. German Giant, Better Boy, Super Marzano, Brandy Boy and Sweet Baby Girl.

Update: I hope I am not boring you all with this information but it is fascinating to me that light bulbs and frost blankets can keep tomato plants alive without heating the GH with -4 OS temps. This is what it looked like this morning - GH temp was 19 degrees - under the frost blanket was 36-37 degrees. It appears the tomato plants were protected, although I think -4 appears to be about the limit low OS temp?!

Only a few lines have been reported to have problems with flowering when there are bright security or street lights nearby. But for the most part the effect is minimal. Especially at this time of the year for most varieties.

The heat to keep them going out ways the set back that might occur from this brief period of uninterrupted light.