* CFO says 2018 results likely to come in at bottom of range
* Osram forecasts FY 2018 EPS of 2.40-2.60 euros
* Affirms sales, core profit forecasts
* Q1 adj EBITDA falls less than expected (Recasts with CFO comment on guidance, sales figures)
FRANKFURT, Feb 7 (Reuters) - German lighting group Osram warned that a recent slide in the U.S. dollar against the euro was making its full-year guidance more ambitious after foreign exchange effects held back revenue growth in its fiscal first quarter.
"We affirmed our guidance for the year, but we have to say that it is a forecast that is certainly ambitious and is probably at the bottom of end of the guidance range," finance chief Ingo Bank told journalists on a conference call on Wednesday.
Osram's forecast for earnings per share of between 2.40 euros and 2.60 euros in the fiscal year through end-September was based on an exchange rate of $1.18 to the euro.
But the dollar hit a 3-year low last month, trading at $1.25 to the euro, after U.S. Treasury Secretary Steven Mnuchin said he welcomed a weaker currency.
Osram generates around half of its revenues in U.S. dollars.
Fiscal first-quarter group revenues rose 3.5 percent to 1.03 billion euros, a tad above consensus for 1.01 billion. Excluding 60 million euros of currency effects, revenues would have been up by 5 percent in the three months through end-December.
Adjusted earnings before interest, tax, depreciation and amortisation (EBITDA) fell 4 percent to 172 million euros, beating an average forecast of 162 million euros in a Reuters poll.
Osram stuck with forecasts for full-year comparable sales growth between 5.5 percent and 7.5 percent and broadly flat adjusted EBITDA of around 700 million euros.
Currency effects, ramp-up costs for its new light-emitting diode chip factory, the world's biggest, in Malaysia and higher spending for research and development will add up to more than 100 million euros for the full year, it said. ($1 = 0.8077 euros) (Reporting by Maria Sheahan and Irene Preisinger; Editing by Subhranshu Sahu/Keith Weir)