when i work on a image then save it as a psd and jpeg the jpeg always come's out a lot lighter I have tried resetting the work space but it still the same.
Does the JPG have Camera Raw settings, by any chance? This has been known to cause preview problems in some versions of ACR. Workarounds included disabling the ability for ACR to develop JPG/TIF, but it was fixed in later versions.
Otherwise, I can't see why they should display differently in Bridge, unless it is related to cached previews and/or embedded thumbnails being out of sync.
I have tried resetting the work space
Resetting the preferences might be a better idea (hold down option -mac- or control -win- when restarting Bridge and choose reset preferences)
This solves most problems but first check if it is not a cache related problem. Select the jpg that is lighter and with right mouse click choose purge cache for selection.
And I think Yammer P does have a point with ACR settings. Check the camera Raw preferences to see if 'apply auto tone adjustments' is checked. If so uncheck it and try again.