As you said, your eyes look tired due to lack of sleep. So, the best way to brighten eyes is get good rest and have a good sleep. Now, if you want to brighten your eyes in a short time. You can make a cup of tea with two green tea bags, then put the tea bags in refrigerator to cool. At last, place the tea bags on each of your closed eyes for 10 to 15 minutes, it will help you remove puffy or swollen eyes due to lack of sleep.
Since you don't have enough sleep, I think sleep is a effective way to brighten your eyes naturally. Then you can apply cold tea bags to help treat your tired eyes. Put cold tea bags on your eyes for 10 to 15 minutes. Two chilled slices of cucumber are also good to brighten the eyes. Apply slight massage around your eyes can make your eyes more energetic because it help promote the blood circulation around the eyes.