Can the morning rays keep the pounds off? You bet! According to an article out of Northwestern University Medical Center published in the April issue of PLoS ONE, morning sunlight for 20-30 minutes between 8 am and noon can lower our body mass index by 20% over time! This means, according to this scientific study, that a 150 pound person would lose about 30 pounds from just morning sun exposure over time.
It takes about 500 lux (the amount of light) to reach the threshhold for this effect to take place; consider that there is only about 200-300 lux with indoor lighting and about 1000 lux on a cloudy day outside.
We also need sunlight to make vitamin D. Because UVB rays are only present between the hours of 10 am and 2 pm, the best time to get both effects would be between 10 am and noon.