how to force OWA light usage

To set the restriction on the Virtual Directory for all users,

Set-owavirtualdirectory -id: -PremiumClientEnabled:$false

To set it for a specific user

Set-CasMailbox -id: -OWAPremiumClientEnabled:$false

how to change Exchange 2007 owa public and private logout time

Private
If you select private option at OWA logon screen,your session will end after 480 minutes,if necessary or would like to change

Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchange OWA
DWORD: PrivateTimeout
Values: 1 to 43200
Missing DWORD = 480 minutes (default)

Public
Public option gives your session is limited for 15 minutes.use this registry key for changing.

Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchange OWA
DWORD: PublicTimeout
Values: 1 to 43200
Missing DWORD = 15 minutes (default)