### Keep up-to-date with Free tutorials!!

- Latest news
- Exclusive Shop Offers
- Preview early content
- Plus much more

Not Ready to take that step? OK, Why not just Subscribe to the RSS Feed

1 | 2 | 3 | 4
Physical Light Exploited

By Florian Wild
| 7080 Views
| 0
Software used:
Maya

Ugh! Exact same result!

This also clarifies why most people tend to set their photon intensity to 10 times their direct light intensity when using Maya lights with quadratic decay. Well, now they know that they actually should either divide the direct light intensity by 4*pi (=~12.566), or multiply the photon intensity by 4*pi. This way, physical_light can safely be 'emulated' in case of point, spot or directional lights.

## Conclusion

Maya light intensity = physical_light intensity / 4*pi (=~12.566)

But what about (flat) area lights? Well, here's a simple point light, with physical_light attached (intensity 10000.000) and MentalRay area light set to true, type rectangle - it's sampling is set to 1/1 and the number of anti-aliasing samples is min/max 1/1 to avoid irregular noise for our test:

Let's try to apply what we learned above. Physical_light detached, intensity divided by 4*pi, decay rate quadratic:

Hmm, that didn't work out. Let's have a look at the physical_light's source code again:

[code] case miLIGHT_RECTANGLE: /* rectangular area light */
mi_query(miQ_LIGHT_AREA_R_EDGE_U, state, light, &u);
mi_query(miQ_LIGHT_AREA_R_EDGE_V, state, light, &v);
mi_vector_prod(&normal, &u, &v);
mi_vector_normalize(&normal);
mi_vector_to_light(state, &dir, &state->dir);
mi_vector_normalize(&dir);
/*
* Compute area-to-point form factor (except cos at
* the receiver). is cos at sender. Returning
* 2 means "no color and stop sampling".
*/
cosine = mi_vector_dot(&normal, &dir);
if (cosine <= 0)
return((miBoolean)2);
if (paras->cos_exp != 0 && paras->cos_exp != 1)
cosine = pow(cosine, paras->cos_exp);
/*
* cos term and distance attenuation. No area term
* since "color" of the light is energy, not radiance.
*/
f = cosine / (M_PI * r2);
break;[/code]

As you can see, in the line next to the last, pi only is used. So let's try that - intensity divided by pi only (10000/pi = 3183.099):

1 | 2 | 3 | 4
Related Tutorials

Tutorial

Florence Design Academy – Basic Lighting Settings in 3ds Max

Keywords: florence design academy, lighting settings, lighting,

(36)
3 37134

Tutorial

Global Illumination for the Beginner

Keywords: global, illumination, beginner, max, lighting,

1 31603

Tutorial

Making Of 'Neoclassic Livingroom'

Keywords: room, walls, chair, table, lighting,

0 9523

Tutorial

Lighting and Rendering in V-Ray - Interior

Keywords: room, walls, chair, table, lighting,

20 50941