IES Light Profiles

IES Light Profiles are a curve that defines light intensity in an arc that Unreal Engine 4 will "sweep" around an axis to make Point Lights and Spot Lights appear to be casting light more realistically, as if accounting for the reflective surfaces in the light fixture, the shape of the light bulb, and any lensing effects. The curve itself can be seen as a multiplier for the overall brightness of the light, as if you were projecting a texture from the light, but with out the texture overhead to do so or the errors that can occur when projecting at some angles.

Where can I get them?

The easiest way to acquire IES Light Profiles is to simply head to a manufacturer's web site and download them, as almost all major lighting manufactures provide them free of charge. Lithonia Lighting and Phillips for example, give a wide selection of light profiles for single lights. And they all document their lights very well, going so far as to base the profile on the type and color of the light emitter used and any variations in the light fixture.

The nice thing about Lithonia Lighting is the website has a web browser profile viewer so you can see what you are getting, once you get down to the actual light you want.

If you examine a profile in the Unreal Editor, they will be represented as a 1D texture (a gradient), however, they are not textures. They are ASCII files containing a wide array of meta data:

IESNA:LM-63-2002
[TEST] 98100505
[TESTDATE] 1/31/2008 
[ISSUEDATE] 1/31/2008 
[TESTLAB]   [MANUFAC] Lithonia Lighting 
[LUMCAT] TPG 1000S PG21 M ( SC=1.5) 
[LUMINAIRE] OPEN GLASS OPTICAL, 1000 HPS W/ MEDIUM DISTRIBUTION 
[LAMPCAT] LU1000 
[LAMP] ONE 1000-WATT CLEAR E-25 HIGH PRESSURE SODIUM, VERTICAL BASE-UP POSITION. 
[BALLAST] 
[BALLASTCAT] 
[DISTRIBUTION] SEMI-DIRECT, SC-0=1.5, SC-90=1.5 
[_LAMPPOSITION] 0 , 0 
[_LAMPWATTAGE] 1000 
[_LAMPLUMENS] 140000 
[_MOUNTING] 
[_FAMILY] TPG 
[_PRODUCTID] 7b5d891e-1c98-4dfa-ae63-b3bef1066d68 
[_INFOLINK] www.lithonia.com/visual/ies/ies.asp?vfile= 
[_PRODUCTGROUP] INDOOR HID 
[_TERCAT] Highbay, Nonlinear 
[_TER] 48 
TILT=NONE 
1  140000  1  21  1  1  1  -1.72  -1.72  1.02 
1  1  1100 
0  5  15  25  35  45  55  65  75  85  90  95  105  115  125  135  145  155  165  175  180 
0 
27438  26506  28483  28459  27031  24803  18881  12112  5247 
5371  5433  5622  5682  5484  5214  4117  3461  2868  1508 
756  382 

The IES Profile for a Lithonia TPG_1000S_PG21_M

Usage

  1. Import an IES Profile either by clicking and dragging it into the Content Browser or by using New Asset -> Import to...

  2. Assign it to a Point Light in the scene by dragging the light profile into the IES Texture slot under Light Profiles.

  3. You can adjust the brightness of the profile by using the IES Brightness Scale slider.

  4. You can also tweak the "texture" that is created by double-clicking on it in the Content Browser to bring up the Texture Properties.

While IES Profiles can be used with lights with their mobility set to Static they cannot be directly assigned unless the mobility is Stationary or Movable. Using the IES Profile with pre-computed Static lighting can sometimes produce artifacts from the mask. It is recommeneded to only use these with Stationary and Movable lighting for the best results.

Spotlights

IES Light profiles basically turn point lights into spotlights (visually speaking) and using an IES profile on a spot light will operate the same way as on a point light except the spotlight cones will mask the IES profile effect. However, since the projection area of a spot light is an 179 degree arc at its maximum, you lose any IES data past that point.

In these images, the light on the left is a spot light and the light on the right is a point light, notice the lack of lighting above the spot light. The spot light's cone clips the IES Light Profile effect as seen in the image on the right.