Soil cables are one option I am looking for other ideas. Maybe a pipe heater? Roof heater? Would they get to hot? I want something to leave on all the time and does not have a thermostat - so it cannot get to hot.

Used to be that cheap incandescent lamp bulbs were excellent heaters. Can't really find them anymore. An LED or compact fluorescent lamp won't really heat anyone up. True that heating mats and cables, as well as heat lamps, are expensive.

I have a couple of ceramic heat lamps. Still pricey, but not quite ridiculously so. Just bond one onto a metal tray.

I thought about light bulbs but they are not efficient and I am hoping for something that rests on the ground. I do use light bulbs in a thermal switch for when it gets really cold.

Thermal switch was not the right name. A thermostat controlled switch with 100 watt light bulbs plugged in.

Light bulbs can be 100% efficient as heat producers. What doesn't get emitted directly as heat (which a lot of does in incandescents) comes out as light, and if you cover the bulb so the light doesn't get out, you've captured that light as heat as well. A covered bulb emits all of its watts as heat. The trouble with LEDs and fluorescents is that they just don't use a lot of watts.

You can rest any bulb on the ground. Ceramic, glass, whatever. They don't care.

dan I had no idea, and I am an engineer. Very very very good info!!!!!!!!!!!!!!!!!!!!!!

But again, the trouble with rope lights is that most of them are LEDs these days, and don't put out a lot of heat. By all means, if you do this, try to find incandescents.

I just bought another rope light to use in my greenhouse, I only saw incandescents on the shelf. The store was having a 40% off sale so these cost me less than $10.

Here's a fairly inexpensive heating pad:

https://www.amazon.com/Comfytemp-Electric-Settings-Shoulders-Washable/dp/B09985XF18/ref=sr_1_50?crid=3ABAZMND1EAVY&keywords=medical+heating+pad&qid=1670537852&sprefix=medical+heating+pad%2Caps%2C137&sr=8-50

Honestly, a seedling heat mat and a thermostat really is the best option. A lot easier to use the right tool for the job than to try to come up with an alternative that may not work as well. I haven't bought any in a while and can't remember what I paid when I did but they are something you buy once and will last for years. They provide gentle heat and are safe and water resistant. Also easy to roll them up and store when not in use.

That said, if you want to go a light bulb route then use either a halogen bulb or look at a pet or farm store. Bulbs meant for brooding chicks emit heat and there are heat lamp bulbs meant for reptiles that would maybe work.

Rodney

It's about temperature. If you can find or make a mat that provides a decent temperature, there is no need to spend extra bucks for something that proudly calls itself a seedling heating mat. Everything that is sold for growers, including lights, if labelled specifically for gardening, are more expensive than adequate alternatives. That's a general rule in the 'biz.