Stack Overflow says:

See also the Wikipedia article.1 EV is 5 Lux. 2 EV is 10 Lux. 3 EV is 20 Lux. Hmmm. It looks logarithmic:EV Lux

-1 1.25

-0.5 1.75

0 2.50

0.5 3.50

1 5.00

1.5 7.00

2 10.00

2.5 14.00

3 20.00

3.5 28.00

4 40.00

(2 to the power of EV, times 2.5)lux = (2 ^ ev) * 2.5;

You can also use Wolfram Alpha, which, e.g., confirms the above math by calculating 10 EV to be 2560 lux.