Some help: Using IES - trying to get shadows in lighting panel

[jeffsalman]

Hi,

 

Would love to hear your input/experience. My question is ... how would you set up an IES light to get the realistic shade/shadow that shows up at the ends of a ceiling tube lights panel (I've attached pic for reference).

 

Should I model and shade a diffuser to put the IES light behind? That's what I figured. But then I think that would also affect the output of the IES light, right (and make it less accurate)?

 

Would appreciate any thoughts on this.

 

Thanks in advance!

[TomD_Arch]

In your example I wouldn't use an IES light. Because you answered your own question: light that passes through a diffuser gets dispersed. In your example, what I would do is literally take your photo and in photoshop cut out one of the light lenses, do some perspective adjusting to the shape and then use that as a self-illuminated material applied to the lens in the model. Then I would create a light plane just fractions of an inch below and set that to create the light at whatever setting you need for a 3 or 4 tube 2x4 lensed light troffer. Finally you want to render your image using setting that are similar to the 3 main settings used to take the photo. Look at the .jpg's properties and see what the f/stop , ISO, and 1/x-shutter speed are set to and use those as a guide to get the correct exposure.

 

 

 

 

P.S. I'm going to give a shot-out to Jamie Cardoso here and his book "Crafting 3d Photorealism" he lays out in the book a great example that taught me, and followed to develop my own techniques for achieving this.

Edited January 16, 2019 by thomas.denney@gmail.com

[jeffsalman]

Thanks for the reply, Thomas! Much appreciated. It also helps to get feedback on my question about the light dispersing through the diffuser. I'm trying a different approach. If it works, I'll share it here, in case it provides any fodder for others' ideas in the future. I was a bit surprised to find out that this isn't as common or been figured out how to model (i.e., accurately modeling a tube light using an ies) over the years. I've seen workarounds, but no way to incorporate an actual ies file (using 3DS and Vray). But that leaves room to explore and come back and share Thanks again!

[Francisco Penaloza]

You have many approaches for this really. But if you are or need to use IES light, then you need to consider that the IES information takes into consideration the light fixture, actually, that's the whole need or use of an IES file, you get physically lighting values, temperature and light fixture shadowing.

Using an IES inside a light fixture is not recommended because you are overwriting its information.

Of course, there are artistic licenses you can take, but this needs to be noted.

 

Having said that, if all that you need is the 'looks' then a workflow as mentioned by Thomas will do just fine.

I usually use a combo of self-illuminated objects with a light plane right under it.

 

You can model that light equipment just like it looks in real life and use some self-illuminated objects or mesh lights and you should get a similar look. This all depends on how much time you have to spend on this.

 

If you are using VRay you may want to take a look at the shadow box shader, this one can be used with a VRay plane light and it creates those soft dark corners.

 

The attached image, I used VRay planes with that soft shadow box shader on them to create the dark areas for this translucent quartz desk.

 

Edited January 16, 2019 by fco3d

[John Dollus]

As Francisco mentioned, an IES file takes into account the entire fixture as it's a measurement of light distribution at a distance.

What you are talking about doing is simulating near-field photometrics. It isn't done because it's insanely computationally expensive, requires a high level of engineering precision to be even close to a scientifically accurate result and the overwhelming majority of people using rendering software are only concerned with getting something that looks great as quickly as possible.

Use the shadow box, layered material w/gradients, or bitmaps to represent the lense and get it out the door and billed.

[Lewis Garrison]

Yeah I've gotten away with just using a simple 2x4 texture of that shadow effect in a Vray light material. Then placing an invisible plane light just below the light to actually light the room.

[Chris MacDonald]

https://docs.chaosgroup.com/display/VRAY4MAX/VRaySoftBox