Accurate Lighting, With IES profiles....Possible or Not ?

[Philip kelly]

Good morning.
I have been setting up a model for a outdoor lighting project. Canopies, poles, street lighting.
I have used the correct profiles of IES, and late evening, or night day light set uo.
But when I render , the lighting levels seem so low they can not be accurate.
Is it possible to get an accurate render out of Corona , or is Vray more accurate than Corona for precise lighting test?

Help would be appreciated.

Thank you

Phil

[dj_buckley]

Is your exposure accurate?

What's the full lighting setup?

I'm assuming you've got a dusk HDRI, and then the IES lights, if you've exposed for the dusk hdri and the IES lights seem low at that point, then it'll be the HDRI thats not accurate

[Philip kelly]

Thank you for the reply.
How do you ensure your exposure setup is accurate.
I have changed it to Vray to see if I can use the vray lighting analysis, but the result is the same.

No HDRI, the base lighting set up sun and sky, no clouds, and time of 5:30am for example as the dusk shot looks the best as it a bus terminal.

[dj_buckley]

Go outside at dusk, take a photo of a similar scenario (with artificial lights) - check what your exposure was?

or just set the lights to whatever you want, the falloff pattern/light distribution of the ies files should at least be accurate even if the intensity isn't

[Philip kelly]

if i do what every i want it's not accurate then ....................

[dj_buckley]

Whatever looks 'right' is often much better than whatever is 'accurate'.

Howver, let's stick at it.  Can you screenshot your exposure settings and the IES lights default settings/values?

I'm assuming sun and sky are just left at default values

[dj_buckley]

if i do what every i want it's not accurate then ....................

Also this is why I questioned exposure first.  You can underexpose or overexpose or correctly expose.  They're all technically accurate (assuming the IES files are accurate) but they won't necessarily look good.

Adjusting the light intensity is pretty much the same as adjusting exposure.  Adjusting just the lights gives you much more control though because exposure is global and the lights are individual.

As I say, the falloff and pattern of the IES will remain accurate so does it really matter if you adjust the intensity to your liking, because all you're effectively doing is the same as adjusting the exposure, just on an individual light.

Something else to add.  How are the materials setup? Where are the IES lights placed in the model?  Are they placed exactly where the bulb would be?  If so does that mean they're behind a glass material that you've made?  How closely does that glass material match the glass material of the actual bulb? etc etc etc

In other words, you can fixate on accuracy or you can just do whatever looks good in a fraction of the time :)

[Philip kelly]

Thanks again for the feedback. I can't put an image up, client NDA.
Light is just above a the glass of the light, I am using IES files provided by manufacturer, and they just seem very week.
The street light setting of the IES seems very low also.

I will keep going and hopefully get a solution. Thank you .
Phil

[dj_buckley]

Can you share the IES file or at least screenshot the IES file default settings, you can blur everything else out.  Keen to know what their default values are

[dj_buckley]

Also for what it's worth, I've just tested a couple of IES lights with Corona and the intensity value doesn't change at all despite them being wildly different lights.

So it looks like it's up to you to dial in the correct intensity.

Most sites that provide the IES files should also tell you the correct lumen value?  This is a good starting point I guess

I've attached an example from the ERCO website

[Philip kelly]

Thank you again, your very good to answer this.
I have brought in the correct IES files and set the Lumen as per the manufacturers settings and on the Data sheets, so thank you , for that.
I have an engineer looking at it now, and it will be interesting to see there take on it, as there are so many factors involved in getting the realistic look,  and its not what everybody sees every day as we walk around in the evening.
I will let you know. I can sends image privately if that is any good.

Phil

[nauticus25]

I've done some lighting studies as well. I'll use IES files when available, and ensure the lumen output matches what was specified by the lighting designer. Assuming you've done that with all your lights, then you can be reasonably confident that the light levels of your various lights are accurate ... relative to each other. That's the important bit to communicate to the client. The overall exposure of the image is an artistic interpretation of what "looks good", just like what your eyes and real world cameras do.

The Corona Sun and Sky have arbitrary Intensity numbers with 1.0 being "physically accurate". We have to assume that the output of the lights relative to the output of the sun is accurate, but I wonder if the devs have any data that can be provided to verify what "physically accurate" means.

The old Mental Ray render engine used to have light meters you could use to verify your light levels. Without light meters in Corona, you don't have a solid data point to hand to your client to back up your claim of accuracy. The best you can do is explain your process and remind them that at best, rendering is an artistic interpretation and that the final result will look different on different monitors, phones, prints, etc.