1. IES LIGHTS
— Quan — Truc – Phuc —

2. Examples of light distribution
Source: solidangle.com

3. IES Illuminating Engineering Society
A standard file format created for electronic transfer of photometric data over the web.
IES file is the measurement of distribution of light.

4. Source: cgarena.com

5. Same render with different IES Lights
IES in 3ds Max
Two built in IES Light: IES Sun & IES Sky
IES Sun: Physically-based light object that simulates sunlight
IES Sky: simulates atmospheric effects
3ds Max also allows to use external IES files through its Photometric Web feature.
Same render with different IES Lights

6. Source: www.cgarena.com
IES Viewer free tool
Source:

7. DEMO