I don't know where "here" is. You didn't say in your opening post. Based on my limited experience with this plant and what I've read they will tolerate getting only a full day of bright indirect light but do better with sunlight. That hour of sunlight is important. You can use a plant light but often for a plant light to make a difference it would need to be placed quite close to the plant, I'd guess about 1 - 2 foot distance, so that the light is intense enough. Considering the size of your plants and the spread of their leaves you'd probably need to get a light for each plant. You might need to start turning on the light further away than 2 ft and gradually decrease the distance from the plant. Too much light too suddenly can sunburn a plant.

Technically, this isn't a palm. It is probably a Beaucarnea and has more in common with Asparagus than actual palms. If you want to research your pony tail palms more then use Google to search for Beaucarnea recurvata.

I use a cool white/ daylight bulb to help supplement light during the winter months. it hangs directly over my Ponytail Palm.