It is a common mis-perception that green tea is lower in caffeine than other categories of tea. It is not. You can read a bit more about this at the caffeine chapter in Tea Guardian:
However, it is not necessarily only caffeine that gives a person a less than better sleep. TCM coldness in things sometimes do that too. For example, if you already have some weakness in TCM coldness, eg, low blood cell counts, shortness of breath, weak digestion, weak liver, during menstruation etc, and then you eat a bowl of cold salad, or a jug of cold beer, or a big piece of water melon close to your bed time, then you may not sleep too well either.
Steamed green tea (not all green tea) is cold in TCM nature. It also has high count of caffeine. So it is better to be avoided after late afternoon, if your body is not up to it.
