Equation 5.10 from Real Time Rendering book

We will use $E_L$ for irradiance perpendicular to $l$

Where $l$ is the light vector.

What does this mean? How do I calculate $E_L$?


1 Answer 1


The line you quoted says it: $E_L$ is the incoming irradiance at the surface due to the light source under consideration. Less technically, it's a vector representing the intensity and color of the incoming light at that point.

The equation you mention is for a punctual light source (directional, point, or spot light), so in this case $E_L$ would simply be the user-defined RGB color of the light source, multiplied by any relevant attenuation factors—such as shadows, distance attenuation for point/spot lights, and cone angle attenuation for spot lights.

  • $\begingroup$ wasn't the original El name derived from "emissive light" ? which was not a convolved term, but an additive term in front of the integral. Irradiance should be named Ir no ? $\endgroup$
    – v.oddou
    Apr 5, 2017 at 9:14
  • $\begingroup$ @v.oddou E is the usual variable for irradiance that I've seen used in texts and papers. Emissive light is usually denoted $L_e$ (L is radiance). $\endgroup$ Apr 5, 2017 at 13:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.