Most of the seeds I grow need about a soil temperature of 70 degrees. That’s what Shaw Nature Reserve uses and what has worked well for me in the past.
Note – I used a Laser Infrared Thermometer to get the soil temperature.
In the past I have used heating mats to achieve this temperature, but I noticed a difference this year since I have started using different lights.
I now use and recommend, Lithonia Lighting, 4-Light Grey Fluorescent Heavy-Duty Shop Light. They use T8 bulbs. I now uses these bulbs close to the seed trays with a plastic cover.
As you can see from the picture, there isn’t much difference between trays with or without bottom heat. In fact the bottom heat tray seems to have poorer germination. I did notice that the bottom heat trays got up to 97 degrees while the trays with just the 4 bulb lights got up to 77 degrees. I eventually turned off the bottom heat since it seemed to be to high.
I probably won’t use my heating mats in the future since my new lights put out enough heat to get seeds to germinate.