* H1 sales down 5.9 percent, Sept trade poor
* Significant risk will miss full-year expectations
* May be affected by liquidation plans of DJ supplier
* Shares down 33 percent by 0905 GMT (Adds analyst comment, shares, details)
By Rhys Jones and Mark Potter
LONDON, Sept 25 (Reuters) - Luminar, Britain's biggest nightclub operator, warned it could miss full-year profit expectations after reporting a fall in first-half sales and worsening trade in September, sending its shares down.
"There is a significant risk that the company will not meet market expectations for the full-year. The outcome will depend to a large extent on trading over the next quarter including the important Christmas period," the company said on Friday.
Shares in Luminar, which have lost a quarter of their value over the last year, were 33 percent down at 87.5 pence by 0905 GMT, valuing it at around 100 million pounds ($159.9 million).
The firm, which runs the Liquid and Oceana chains, said sales from continuing operations fell 5.9 percent in the 26 weeks to Aug. 27 and were down 4.5 percent on a same-outlet basis, stripping out the effects of a late August bank holiday.
Admissions revenues were down 0.2 percent, footfall was down 2.9 percent and drinks revenue down 6.6 percent. However, gross profit margins improved, due to higher drink prices.
Luminar blamed rising unemployment among the young for its drop in sales after Britain's jobless figure rose to 2.47 million in July -- its highest level in 13 years.
Prior to Friday's trading update, analysts were, on average, expecting Luminar to report a pretax profit of 17 million pounds for the year to the end of February 2010, according to a Reuters Estimates poll of 11 analysts.
Evolution analyst Nigel Pearson cut his 2010 pretax profit forecast for Luminar to 13 million pounds from 17.4 million.
"Even more than usual, Luminar's year will be defined by the Christmas quarter which kicks off with the return of students and freshers' week next month," he said.
Luminar also said that it might be affected by the decision of Eminence Leisure Limited, in which it owns a 20 percent stake, to look at a creditors' voluntary liquidation.
Eminence supplies Luminar with DJs and performing artists. (Editing by John Stonestreet and Rupert Winchester)