How to calculate LED light output

I’m trying to assemble an array of LEDs to be configured as a solar simulator. I need to compare this array’s output to the solar spectrum as a function of W/m^2/nm.

To do this I need to go through datasheets of LEDs on sites such as Farnell, Digikey, etc. I am having trouble figuring out how to convert the units given in datasheets.

For example, if I have an LED that states typical lv (cd) @ 150 mA = 4.2, and Phi-v @ 150 mA = 12, at 120 viewing angle and 625 nm, how would I find out the W/m^2/nm? An arbitrary distance of 10 cm is set.

Datasheet of above example: http://www.farnell.com/datasheets/1776464.pdf