Mr Stephen will address the conference on Saturday

Leader Nicol Stephen also said the tide was moving towards more powers for the Scottish Parliament.

His comments came ahead of the party's first major conference since the SNP formed the new minority government.

Mr Stephen told BBC Scotland that the Lib Dems' effectiveness as an opposition group was growing.

The party also said it was committed to transforming Scotland into a European green energy "powerhouse".

Speaking ahead of the Scottish Lib Dem spring conference in Aviemore, Mr Stephen said there was now a "renewed sense of confidence and optimism" in the party, which served in two coalition Scottish administrations with Labour.

Citing recent council by-election successes and a "growing reputation" for effectiveness in parliament, he told the BBC Scotland news website: "In terms of the powers of the Scottish Parliament, the world is moving our way.

We want a second Scottish Enlightenment Nicol Stephen Scottish Liberal Democrat leader

"We must take this chance, we must seize this opportunity. We want powers for a purpose.

"We still have single ministers in Whitehall who expect to control the lives of tens of millions of people from their desks."

Mr Stephen said the defining principle of the Lib Dems - which refused a power-sharing deal with the SNP over the issue of independence - was more power for people over their own lives.

The former Scottish deputy first minister added: "It is simply not acceptable in a modern democracy that one parliament receives a cheque for £30bn from another parliament, with its sole responsibility being how to spend the cash."

Conference speech

Politicians, Mr Stephen went on, had a responsibility to tackle climate change.

"The Scottish Lib Dems have already set out our plans for 100% renewable electricity in Scotland by 2050 and want to make polluters pay through a system of green taxes.

"Liberal Democrats have a drive and a determination to do much for Scotland," said Mr Stephen, who will deliver his conference speech on Saturday.

"We want the next 100 years to be a liberal and democratic century. We want a second Scottish Enlightenment."