The Lightning network is still highly experimental. Because of this, users of the Lightning network should not commit significant funds to Lightning channels.
Currently, this is enforced on the software level by limiting the maximum channel size to 0.16 BTC.
This maximum value that Lighting users are able to commit to channels in the future will likely be raised when there is a consensus that it is safe to do so. For now, you will get an error when attempting to open a channel for an amount larger than the current network maximum.