Lewes is an unusual atmosphere at night, with most pubs serving both the younger and older crowds simultaneously and in harmony. It is not unusual for the newly legal 18 yr/o to be seen sharing a pint with their parents at the same bar! There are, as with all places, the exceptions, but Lewes is a extremely safe place to be at any time of day or night, and the locals are friendly and accomodating. With pubs closing nationally, Lewes is no exception, and as pubs close, they are reopened by new owners, bringing with them a different atmosphere and attracting different clientele. The Lewes Arms, Dorset, Snowdrop, Black Horse, Brewers and Gardeners are all currently more quiet pubs, in volume rather than customer traffic- in fact the Lewes Arms is often bustling with people, where as the Elephant and Castle known locally as the Elly, Lansdown, Lincolns and the Lamb are often regarded as the more busy and loud pubs... but again this is constantly changing. The only pub in Lewes that seems to stay the same is the infamous Tally Ho pub situated on the outskirts of the main town at the edge of the Landport housing estate. Frequented almost exclusively by Lanport residence, it is the only pub to maintain a constant "bad" reputation. In reality this pub is just another Lewes pub, but because of it's limited clientele, can feel quite intimidating to newcomers; it however has a brilliant atmosphere during big sporting events, especially anything to do with football!
Check Viva Lewes (http://www.vivalewes.com/home/) for info on "nights" held in local pubs, often featuring folk music, DJs and the such. Also be aware that cafes in town occasionally open late and host event nights- the Needlemaker's cafe is particularly good for this, try to catch one of their world nights which include music and food of a particular country theme- great fun.
The youth of Lewes tend towards the more bohemian and creative than obnoxious and urban, and as such, tend to create their own fun within town. The mostly unattended industrial estate in town has become a recent hotspot for those under 30 indeed anyone from the age of 15 upwards really with warehouses being comandeered to house parties. Do not be overly cautious with these events, as they are probably not what you would expect from a youth illegal party- these tend to be less about drugs, rave music and bad behaviour, and more about live music, art, and the occassional pizza oven!!
The night life is essentially pubs and restaurants, but Brighton is 20 minutes away by train, a little more by bus, with all the varied and often loud and bustling night life that you could ever ask for. Taxi's will take you to and from Brighton, but expect to pay £20 upwards for each journey.
Harvey's bitter
(http://www.harveys.org.uk/). one of the oldest independent breweries is right in the middle of town. sample their wares at the john harvey tavern (http://www.johnharveytave...), or get take-aways from the brewery shop on cliffe high street. fine wines, too.