Turtles/Indian star tortoise won't bask in Sun
I have three Indian star tortoise (all females) which are about 3.5 inches in size.
I keep them indoor in a 3 x 4 wooden enclosure with a water dish, basking area (with a 75 watt heat bulb), heating pad, a hiding box and garden soil for moisture. Their diet consists of 90% grass and other greens and 10% vegetables and fruits. Also I feed them once at night every day.
It's very hard to find a UVB basking lamp where I leave, so as an alternative I leave the tortoise in the sun for 2 - 3 hours each day so they can get enough sun light.
The problem is that they don't stay in sun, I have another 3 x 3 wooden enclosure which I leave in my balcony. I put the tortoise in this enclosure and they just run and hide in shade.
They don't stay in sun not even for few minutes. I tried leaving food in the enclosure but failed. I also try leaving them in a water tray so they can bathe and stay in sunlight but after few minutes they just climb out of the tray and hide.
I also tried early mornings, afternoons, early evenings but they just won't stay in sun.
Is this normal? can you please let me know how can I get them to bask in sunlight?
Also they drink little water and rarely bask in the indoor basking area as well. They just eat and sleep...do nothing else. Is this normal?
I am thinking of growing grass in the outdoor enclosure will this help?
I live in east part of India where temperature ranges from 85 - 90 F.
UVB rays will penetrate shade and cloud cover, so I wouldn't worry about that too much. They can overheat quickly in direct sun, and smaller tortoises don't like to be in the open for long because their instinct is to hide from predators, so their behavior is pretty normal. As long as they're outside, they'll be getting some UVB.
I would try to give them more room if you can. Something at least 4 x 5 would be better, and keep in mind that they will need much more room as they grow. I would also get a thermometer and check the temperatures. They need a basking area with 90-95 degrees (measure on the substrate, not in the air), and then a cooler area that's around 75 degrees. If it's too warm, try giving them deeper substrate so they can dig in and cool themselves off. If they're too warm, they won't be too active.
I would also stop feeding vegetables and fruits. Star tortoises are primarily grass and cactus eaters, with some leafy greens (weeds). Growing grass in their outdoor enclosure is a good idea. You didn't mention if you're soaking them, but they should be soaked in lukewarm water for 15-20 minutes two or three times a week. This helps to make sure they stay hydrated.
All in all, it sounds like you're doing a good job with them. Keep making sure they get some hours outdoors, and they'll be fine with the amount of UVB they get.