VFX Understanding Photometric Lights -

Understanding Photometric Lights

Photometric lights are one of the most convenient way of simulating real world lights for photo realistic lighting and visualization.

In physical terms, the word Photometry means measurement of light terms of energy interactions. Light consists of energy packets called photons. These photons interact with surfaces which absorb or radiate out the same .

Photometric lights follow the inverse square attenuation rule i.e. light intensity decreases in proportion to the square of the distance from the light source.

In max there are 4 photometric light distribution strategies:
1. Isotropic-In this method, the light percolates and spreads in all directions
2. Spotlight- Simulates a focused beam of light
3. Web-This allows the user to use web files created by light manufacturers (IES map files)
4. Diffuse-This distributes light from a surface with the greatest intensity at right angle to the surface.

The photometric lights available in max are target point, free point, target linear, free linear, target area, free area, IES sun and IES sky. All of these are pretty self-explanatory.

However let me elaborate a little on IES sun and IES sky.

IES sun: This is a special type of photometric light, which simulates sunlight. It can give good results when used along with the Daylight system in max. It has a target object and a look at controller. I test rendered a simple teapot scene in Max, using the 3 point system, IES sun included. Using scanline,it gave neat results.

So much so, that it gives results close to radiosity, without having used advanced lighting system. Heres the same scene, I rendered using one light, and radiosity( results don’t differ much)

IES is a specific kind of light used especially in architectural visualizations. In 3ds max those files, which describe intensity of the light in 3d dimension, are loaded into photometric lights

Some light manufacturers also develop light information IES files, which can be used for web photometric light simulation.

Heres a small test scene rendered I scanline,with only 3 web photometric lights.


For those who are new to IES lights, let me explain

Set up your test scene like I did. Then under the lights drop down menu, choose Photometric.

Select a free spot. Now scroll down to distribution. Set it to Web. Now for the intensity, check multiplier (set to 50%). Under web parameters, select the IES web file.IES web files are available at sites like http://www.erco.com, can be downloaded for free.

These are the settings I used for the above scene.

Interestingly I came across a software, which helps me make my own IES date file.

It is called IES generator3, which again can be downloaded for free at http://riproductions.no.sapo.pt/galeria.html.

This is how the interface looks. Very easy and self-explanatory.

IES generator

Here the graph towards the left is modified to create the IES data file that you see to the right. For the above test scene, I have created the IES file in a similar fashion.

For those who wouldn’t want to create their IES files, they can use the free files available online.

Similarly, these IES files can be used with GI renderers like mental ray ( version3.2 and above) ,vray, brazil, final render etc. However Maxwell doesn’t have its own lights – each light must be made by your own. When we have to make simply area light – it is an easy thing. We just create plane and assign light shader to it.

One good tutorial I came across is http://www.evermotion.org/index.php?unfold_exclusive=91&unfold=exclusive, where it is nicely explained as to how one could get renders similar to ies files.

Interestingly, I have always loved using IES lights with vray.Again,this little information about IES in vray is directed towards those new to vray,and exploring.,let me brief you through one quick IES test scene,rendered in vray.

Set up your scene, the way I did. It’s made out of simple boxes and teapots. Assign the desired material to the objects. Now it’s the time to add photometric lights. I chose free point this time. Set the lights on the top of the models (tea pot in this case). Set the distribution of free points to WEB.

Choose your web file. There are plenty available at www.erco.com

You will notice that once you add the web file to the lights,the shape of the light changes,according to the ies data. Set the multiplier as per your requirement,the same way like you set the multipliers for your normal lights. These are my settings for the scene.and this is the wireframe.

For vray settings,I have enabled GI,and used QMC as my secondary bounce. You may use light cache or photon map.

Room model coutesy ( http://evermotion.org)

Enjoy playing with different IES data files!