A source emits 12.0 J of lightof wavelength 620 nm and 8.0 J of light of wavelength 580 nm per second. The relative luminosilty at 620 is 25% and that at 580 nm is 80%. Find a the total radiant flux, b. the total luminous flux and c. and luminous efficiency.

Explanation

AS. The total radiant flux = Total energy radiated per unit time =12J/s+8J/s=20 J/s=20w.
b. The luminous flux correspoinding to th 12 W of 320 nm radiation is
`0.35x(12W)xx685luen W^-1=2877 lumen.`
Similarly, the luminous flux corresponding to teh 8 W of 580 nm radiation is
`=0.80xx(8W)xx685lumen W^-1 =4384lumen.`
the luminous flux of the source is 2877 lumen +4384 lumen
`7261 lumen ~~7260 lumen.`
c. The luminous efficiency =(Total luminous flux)/(Total radiant flux)`
`=(7260lumen)/(20W)=363 lumen W^-1`