[Radiance-general] A modern comparison of Radiance and other rendering engines

[Lars O. Grobe]

Hi,

there are even more renderers, e.g. pbrt/luxrender, mitsuba, ....

I think the main difference is - that the difference is not known. In 
the Radiance universe, a lot of work is spent on testing the validity of 
the models and methods. This allows professionals to rely on the 
software, as long as they are within the boundaries of the validations. 
There is a lot of other software capable to solve the global 
illumination, but few people will rely on it for quantitative studies 
before they have been validated.

Another, really important reason that people stick with Radiance 
regardless what exists "out there" is that for daylight simulation, a 
good renderer does not help you without the ecosystem of tools making it 
a useful simulation environment. So to make use of climate data, perform 
annual simulations, model the often exotic properties of fenestration, 
and analyze the results, you need more than the ray-tracer.

Finally, what may appear as an advantage - the quick introduction of new 
features and state-of-the-art rendering algorithms, can become a serious 
drawback. The "modular" renderers out there, e.g. Mitsuba, allow to 
combine different modules. Other, often commcercial renderers, may bring 
new features with every release (and may not even tell you if something 
changed). However, if you need to redo all your validations with every 
combination of such modules, or any change in your implementation, you 
hardly reach the point where you can make use of the software.

So while there exist lots of codes to trace light, the motivation of the 
developers usually is not to ensure valid quantitative simulation for 
building performance analysis. In fact, most software in this field is 
based on tuning and adapting good-old radiosity.

https://www.janwalter.org/RadianceVsYouNameIt/radiance_vs_younameit.html

This is an impressive coverage of rendering engines! It just lacks the 
numbers. So while images may look similar, we do not know about 
quantitative agreement.

Cheers,
Lars