A follow-up with the Sun Jar. After I got the jar, i noticed that there are 2 potential improvements: (1) I like it to be brighter; and (2) it doesn't last long enough (only around 5 hours even when fully charged. I prefer it to last the whole night).
Finally have time to disassemble it today and found that the rechargeable battery is only of 700mAh... -.-... no wonder... Replaced it with a 2700mAh battery... will see how it go. But of course, the question is whether the charging circuit efficient enough to fully charge the 2700mAh during the daytime.
(The circuit on the right is my experimental trial on a different approach to test if it can get a better result... both the light intensity and number of hours it can last)