Height of central pole: 2m high for diameter 3m tent 2.5m high for diameter 4m tent 3m high for diameter 5m tent and 3.5m high for diameter 6m tent. The central pole has a ring that you can hang the light. It is all a personal choice what size you go for but as a general rule: If regularly accommodate 1 or 2 twin size mattress a 3 meter is fine. (Please kindly note 3 meter tent cannot accommodate double size mattress) If regularly sleeping 2~3 people and occasionally four a 4 meter will be fine. If regularly sleeping 4+ people or if you are planning on going on extended week long camping trips where set up time/carry weight is not such an issue a 5 meter is better suited as it gives you that extra room. If regularly sleeping 4 people both 4 meter and 5 meter are fine. However on balance a 5 meter may be better suited as I would suggest that having slightly more space than you need is not a bad situation to be in. Windproo