Accurate, real world lighting and exposure? Tweet

[pcoombes]

Hi

I've been trying to get real-world values for lights and camera exposure in Octane, but it seems pretty arcane in Octane.

What's the best workflow to ensure accurate camera exposure and lighting in Octane?

The hoops you have to go through to get the correct values for the lights seem particularly unfriendly - see the thread below.

viewtopic.php?f=30&t=42275&hilit=lumen&start=10

This quote from the manual sums things up nicely - "Light efficiency is a beautiful and interesting topic, even if it's cumbersome in Octane, it will add a lot to your renders."

So my request for the developers would be to have all the calculations which you have to go through as shown in the above thread, embedded in the light tag. That is, be able to specify lumens or watts or candelas or any of the usual values, the type of light (LED, tungsten, etc.) and have Octane do the maths. Can't be too tricky, surely.

Whilst we're at it, can we have the Octane camera mimic real world cameras? That is, link f-stop, ISO and exposure time. At the moment the only way to control camera exposure in Octane is to slide the arbitrary Exposure value up and down.
Is this value going up in EV increments/stops?

Sorry, all a bit ranty. I really like Octane. I just want a bit more real-world methodology.

[jayroth2020]

The Power value equates to watts, so if you want to replicate actual physical lights, it is merely a matter of entering the wattage desired in the Power value of a given light. You will still need to adjust the color temperature as desired. The documentation revision will be updated very soon, and this information is covered in that revision.

[AWOLism]

I just wanted to add to the conversation that I agree with pcoombes that being able to choose between lumens/watts etc in the light settings, as well as an easy way to se light directionality (as I recall for instance Vray having) would be awesome. Same thing with being able to mimic camera real world camera behaviour with ISO etc, would be great to have that option. Just makes everyday rendering life a little easier.

Anyway, just my two cents.
Looking forward to updated documentation by the way!

[pcoombes]

The Power value equates to watts, so if you want to replicate actual physical lights, it is merely a matter of entering the wattage desired in the Power value of a given light. You will still need to adjust the color temperature as desired. The documentation revision will be updated very soon, and this information is covered in that revision.

The problem with such a crude, single value is that it doesn't differentiate between different lighting methods ie. LED, tungsten, sodium etc.
A 9w LED light and a 9 watt filament light produce very different amounts of light, hence the manufacturer's use of lumens, candelas, lux etc. which tells you how much light a luminaire is producing regardless of wattage.

I've been using the information in the forum post (link in the original post above), which does seem to provide accurate results, but the fact that it's buried away in a forum thread and requires cross-referencing another couple of sites, means it's not particularly user-friendly. Is the updated documentation going to include that information?

EDIT: Did you mean the wattage value is the power consumed or the power emitted? EG a 100w filament bulb emits only 2-3% watts of light. If it's the power emitted, then that would be more accurate. The problem then would be that very few manufacturers provide luminance values in those units.

[pcoombes]

I've just read the updated documentation and it seems pretty much the same as before.

LIGHT SETTINGS TAB

POWER
The Power attribute value represents light energy in Watts.To get a realistic render render output, enter real world light wattage values into the power setting, representing the proper values for the desired light source. For example, standard bulb wattage typically has a range of between 25 to100 watts and radiates a brightness of about 250-1600 Lumens. In this same range of lumens, Halogen bulbs are 18-72 watts for the same brightness as standard bulb. LED bulbs fall into the 4-20 watt range for standard bulb brightness. Of course, any value can be used, but if realistic results are desired, it is best to stick with known wattage values.

So the question is still how do you differentiate between a 20w Halogen/filament and a 20w LED in this system?
The attached image and file illustrate the issues.
The light on the right has a value of 8.6 watts. The light on the left has a value of 60 watts. If the left light is supposedly a halogen/filament light and the light on the right an LED light, they should be of similar 'brightness', so how do you tell Octane that?

The c4d file also has some lights with correct values for the LED light as calculated using the info from bepeg4d - many thanks!
viewtopic.php?f=30&t=42275&hilit=lumen&start=10

[jayroth2020]

Regarding lights of different types, halogen vs. LED in your example, you need to look at the actual illumination output, as you know, moreso than the wattage. I find this chart helpful:

It is from this website: https://www.homelectrical.com/cfls-vs-h ... led.6.html

The user interface is very general in regard to situations like this. Fortunately, you can dial in the settings as required (setting color temperature, for example) and use information such as that in the referenced chart to balance out the results. There is plenty of information online for lighting fixtures that can be used effectively within Octane.

Obviously the lumens are different per watt of the various lighting technologies. Since we are dealing with watts in Octane, I would use the equivalent lighting information. In other words, if an LED light of 20W produces a practical out of 100W (not 20W), then use 100 for the power value and adjust the color value for the LED.

[whersmy]

Regarding the speed/ease-of-use, wouldn`t it be handy to just have an extra tab/slider/node in Standalone where all of these seemingly complex conversions are already done? So you can just select an emission type/bulb type/Watt amount if you have to light an interior.

[Lewis]

Agreed, Lumens (and LUX in some cases) are only proper way for lighting settings, Everything else (especially Watts) it is crude and inaccurate approximation.

So yeah if possible it would be good time to switch to Lumens internally especially with IES/LDT light files usage which contains exact lumens/candelas value inside the file (which octane IES loader should interpret on loading and adjust settings automatically).

[pxlntwrk]

hi,

All this goes hand in hand with the implementation of a "real" physical camera, of course

[jayroth2020]

I'm not arguing against a lumens-based UI, but that is not what we have today. I am trying to help you get to where you want to go with this using the existing toolset as it is.