how to use photometric lights in vray?

[Tim Saunders]

vray lights have been treating me great for interiors, but i would like to use some of the nice wall washing effects you get by using ies files. when i render i always get an all black render. the only way around it is to crank up the intensity, but then i only get the part where the light is shining, no gi. i have tried qmc, photon map and light cache secondaries. i have even tried increasing the diffuse multiplier in the vray light properties with no result. what am i doing wrong?

[martincg]

this tutorial could help you:

 

http://www.evermotion.org/index.php?unfold_exclusive=86&unfold=exclusive

[Crazy Homeless Guy]

.........are you using exposure control?

[Tim Saunders]

travis,

i tried either way and it didn't make any difference. i'm checking out that tute to see if i can apply the same settings. i did notice that if i added a vray light in the scene for general illumination, the scene of coarse lights up, and i can see the wall washing of my ies lights. but if that is what it takes to see the lights, i am probably not getting any gi from them?

[martincg]

could you send any preview or simplified scene?

[Christopher Nichols]

I talk about IES lights in my new DVD. A few things to check, make sure you are using a real world scale, switch to inches or cm, if your ceiling is 20 meters instead of 2 meters you will have an issue. Even with that, you may need to increase the multiplier by around 400%. Next see that you are using a gamma corrected interiors

[Ismael]

Even using a "real world scale", you should know that the Physical Scale value of Viz/Max exposure control is always active. Even if Viz/Max exposure control is unchecked, the value in the Phys Scale will still affect the intensity of the light. Do a test dissabling Viz/Max Exposure check. Just a box room with a default free point photometric which usually comes at 1500 CD. Render with low Vray settings for speed. In the Physical Scale box of Viz/Max try 1500 first, then 3000 and finally 1.

 

Then, if you please repply what did you notice?

 

Ismael

[Tim Saunders]

yeah, huge difference ismael. so i guess the question is, what scale do i choose? i mean if i am trying to reflect reality, what is real scale? should this even be an optional adjustment?

[Ismael]

Actually, I don't know how this has escaped me for so long! The best thing as far as IES, I suppose is to maintain the rule to set that number to the value of the highest light used in candelas. Of course, what happens when you throw in Vray Lights in a mixed environment? In the end you be the artist.

 

I prefer to use Viz to calculate a rough light analysis of my distributed light as "physically correct" as possible and from there at any event I will use my knowledge of the brightness I should perceive each surface.

 

Take care,

 

Ismael

 

Edit:****************

 

As far as the option part, this is not a Vray issue because Viz/Max do this with their renderer too. Maybe Chaos Vray could do something about it.

[Tim Saunders]

As far as the option part, this is not a Vray issue because Viz/Max do this with their renderer too. Maybe Chaos Vray could do something about it.

 

or even viz/max. but if they were to change it i guess in my opinion it should defalt to the highest light value in the scene, or maybe that method does not always work. no big deal really.

[Hao La]

Make sure you rotate the IES light correctly and try not to place it intersect the wall.

[Ismael]

How about IES and photon map secondary? Try this: Place IES distribution luminaires in a scene. Take note of their candela values of the highest luminaire. Set Viz/Max Exposure to uncheck but set the Physical Scale to like 10. Set Photon Map for primary and secondary GI with check on convert to Irradiance map. Set it so it saves to a file and let it calculate.

 

Now set Secondary GI to Photon Map "From File" and Primary GI to Irradiance. Also set Viz/Max Exposure to Enabled Logarithmic and the Physical Scale to the candela value of your highest intensity luminaire. Render and that is that.

 

Have fun with it,

 

Ismael

[Christopher Nichols]

Vray's photon maps only work in these three conditions:

 

1 - a direct light with no decay

2 - vray lights

3 - a spotlight with an inverse squre decay and a start of 1 max unit.

 

Basically photon maps don't work with eis lights in vray. Use lightcache instead.

[Ismael]

Why not? Using them that way I do get photons splatered all over my scene, so what is it that does not work? I do understand what IES is for, but many people just also trow Vray lights all over the place, like flat planes on windows and such I am sure they are not going through all that theory Vlado gave about the "Physics" of a Vray light. In the end, we will do whatever it takes so that it looks good. Now, if Vray were to implement some Lighting Analysis tools; maybe I will "see the actual light..." like in Lightscape and Viz/Max for that matter.

 

Ismael

[Ismael]

Got this old scene with 10 photometric luminaires and did this experiment:

 

http://img261.imageshack.us/my.php?image=kitchenphotontest8rk.jpg

 

Does not look too bad I think. Just recently got a new LCD monitor and not quite sure about that gamma thing, however I did use that new "Linear Worflow Curve...".

 

Hopefully it uploads fine,

 

Ismael

 

It uploaded good! Used the photon sec as stated and "Very Low" Irradiance.

[anvaraziz]

be sure to work on real world scale,,

 

for me, im using cm, and it works fine.........

[ipdesigner]

be sure to work on real world scale

*i agree, but for me i am using meters.

*since fakesioty i am already using 'phometric-free point light' for IES same thing with vray, there's nothing difference aside from the timeframe but it worth waiting:)

[Tim Saunders]

its going to sound stupid, but what do you mean real world scale? by defalt my scenes are set to us standard feet in the units setup. is that what your talking about? does anyone not do that? and i don't mean us vs. metric.

[ShaunDon]

I work in decimal inches... have never had a problem using photometric lights with VRay. Though some of my coworkers have tried to use them in their jobs and struggled. Not sure where the disconnect is... Are the IES files hardwired for specific unit scales?

 

Shaun

[Tim Saunders]

Old thread yes, sorry. I'm still not satisfied. Here's the thing, there are 2 references you usually hear people talking about physical scale. 1-units, 2-physical scale in exposure control. I figure everyone models in physical units (feet or meters) not generic units. If not, they should. About physical scale in the exposure control, I always turn off exposure control in the environment panel. Is that wrong? The reason I'm asking all this, is because I am asked at least quarterly to do a lighting analysis. In the past, I have just used radiosity and worked it out. That is no longer an option. Has anyone figured out how to get the ies lights to render how they actually will appear in real life? Any time I use ies lights, they are way too dim. Most the time, I just use the lights for effect, so I don't care if the intensity is acurate. When I am doing a lighting analysis the lights need to be acurate as the manufacture specifies. Any tips?

[Crazy Homeless Guy]

Old thread yes, sorry. I'm still not satisfied. Here's the thing, there are 2 references you usually hear people talking about physical scale. 1-units, 2-physical scale in exposure control. I figure everyone models in physical units (feet or meters) not generic units. If not, they should. About physical scale in the exposure control, I always turn off exposure control in the environment panel. Is that wrong? The reason I'm asking all this, is because I am asked at least quarterly to do a lighting analysis. In the past, I have just used radiosity and worked it out. That is no longer an option. Has anyone figured out how to get the ies lights to render how they actually will appear in real life? Any time I use ies lights, they are way too dim. Most the time, I just use the lights for effect, so I don't care if the intensity is acurate. When I am doing a lighting analysis the lights need to be acurate as the manufacture specifies. Any tips?

 

....are you working in linear color space?

[Tim Saunders]

I'm not very versed in linear space. that is a term I have heard a lot more of than I have actually researched. Are you referring to linear color mapping or linear exposure control?

 

BTW, thanks for replying.

[Ismael]

Get you a light meter. Then train your rendering technique to quantize to your measurements from a perception standpoint.

 

Ismael

[Crazy Homeless Guy]

I'm not very versed in linear space. that is a term I have heard a lot more of than I have actually researched. Are you referring to linear color mapping or linear exposure control?

 

BTW, thanks for replying.

 

linear color mapping on the vray roll-out.

 

linear color space can be difficult to understand, but fortunately, the folks at chaos group made it easier with the current release of Vray(1.5). ...it is worthwhile to understand, and i would guess necessary if you are trying to use IES at their spec'd settings without increasing their intensity.

 

basically, your monitor is set up at 2.2 gamma, and real world would be 1 gamma. the gamma of 2.2 makes things appear darker than they actually are. so when you place a IES light, it appears really dim in the scene because of the gamma curve applied top your monitor. to make it appear brighter, the logical thing to do is to increase the intensity, when in reality adjusting the gamma might be the proper solution.

 

the attached file is a room that is 15'x15'x10' with a semi gloss paint, acoustic ceiling tile ceiling, and a stained concrete floor. i dropped 4 -75 watt IES that were included with Max to light the scene. i left the IES at their default intensity values. the cube is 4'x4'x4'

(point_recessed_medium_75w.ies)

 

the first is with linear color mapping, the second is without. i don't know exactly how bright the room should be with 4 recessed 75 watt bulbs. i think there are plug-in Max light meters that may help. ....anyone have any idea?

 

for further reference, i am using a vray physical camera with 200 speed film, a f-number of .7, and a shutter speed of 1/125. i got those settings from this site..

http://www.robert-barrett.com/photo/exposure_calculator.html

..and my paint colors are, Sherman Williams Banana Cream, and Jamaica Bay

http://www.colorcharts.org/ccorg/resources/colors.aspx?ProductID=624&CBN=0AUE-7X2L-HWT1

http://www.colorcharts.org/ccorg/resources/colors.aspx?ProductID=624&CBN=2TM5-URCL-YNC9

 

unfortunately the resident genius on color mapping hasn't been around the board lately. i am just a rookie at linear color space, so i am not backing up anything i said as being correct or definetive. ....take it with a grain of salt.

[Guest nazcaLine]

i had this issue too with ies lights in vray.

i use these lights mostly for their walllwash effect.i use system units=meters, and display units=centimeters, because i import drawings from autocad (that are made in meters).when i use scanline, there's absolutely no problem, i put ies files in the web distribution of the photometrics lights and it all works fine.

but then, i change the render engine to vray and nothing happens.nothing!!

all black!!!

next, i change the same scene to system units=centimeters.(of course, i have to scale the whole test scene) and guess what??? it works!!!

idon't understand!! i tried with inches in system units and it works really fine!!!

why vray doesn't work with system units=meters, if these same lights in the same scene work well in scanline???