Is this sun damage on seedling?

Thin stems on baby plants is normal, your plant "knows" what it is doing. Moving your light to 47 inches away, assuming you are using a LED light will however cause your plant to stretch excessively and that will cause thin stems that are unable to support the plant. With an LED light, roughly 24 inches for seedlings is a normal distance. The leaves on your cannabis seedlings look fine to me, with no obvious problems, more often than not, the first few sets of leaves will have unusual markings or be of unusual shapes, while primarily trying to establish a root system. At this early age, the plants can be thought of as growing in reverse - the leaves first function being to provide energy for establishing a good root system and "anchor". Once the roots are somewhat developed, growth returns to being more conventional, whereby the roots power the above ground plant growth, in conjunction with photosynthesis obviously. Remember too, no plant will ever have 100% perfect leaves, 100% of the time. Cannabis has been growing wild for Millenia, they are not afraid of strong sunlight and can cope with 40+ degrees Celsius from birth, so long as ever the soil is moist, and not suffer any damage or other problems. Your plants look normal, but bringing the light closer, if you are indeed using an LED light, should not do any harm, as long as the substrate is moist and you have good air circulation. Your cannabis seedlings will also need transplanting soon, there is barely any room in those small cubes for root growth and this can stunt your plants rather quickly, especially if they are autos. Hope this helps,......... Organoman.

How powerful is your light? At that age I'd be using a T5 about 6 inches from the canopy

The cannabis seedling looks healthy to me? What specifically are you observing that makes you think light damage? Cannabis needs more light than any other harvested plant (except for maybe some cacti). So I would not be worried about excess light at this stage. The plant leaves will fold themselves to reduce the angle of incidence of light, if they are receiving too much. I can't see that here, nor can I see any leaf burning. The stem is very thin normally at this stage, but if the seedling does not receive enough light it will stretch upwards and become so thin it falls over. Yours looks fine to me, but since you moved the light away just keep monitoring it.