How does one match irradiance to Luminous Intensity in Candela of source?
Optical geometry.

Emitter: 5mm D LED say 65mW ~ 100mW
Assuming +/- 30 deg Lambertian response below half power
Target: 0.01m² =  100 mm x 100 mm square or some equiv round area.   

Calc:  LED Emittance= input (0.1W) Pwr * ζefficiency(?) / Area/ wavelength[nm] = 0.1Wζ/385 nm/π{2.5 mm}²/ = 13.25 * ζ W/m²/nm

Irradiance ratio of spreading light from π*{2.5 mm}² into 0.01 m² = 0.01/1.96e-5= 509

Thus 1 LED = 13.25ζ/509 but you need 1.6
so you need 1.6*509/13.25ζ=  62/ζ  LED's but ζ may be only 10% ??