What is real?
This is a bit psychological and also loops back to the initial problem Vermeer tries to solve as everyone experiences reality on their own and therefore differently.
If we would like to be more objective, we need to tackle things in a bit more scientific way. Luckily a lot of work has been done in that field even before the first image was rendered on a computer. Scientists have always tried to describe reality while leaving out subjectivity. There are a lot of different units and ways to measure light for example: based on the brightness of the light emitter itself or on how bright a surface gets in a certain distance. Besides power, with lights you also would want to measure the color, the shape of distribution, etc.
We can measure these details in a lot of different ways: there are of course super scientific methods to get really precise numbers, but to not over-complicate things in our case a method for measurement with a +/- 5% deviation from reality would already be a big step in the right direction and these type of measurements can be already done in an easy, fast and cost effective way.
How it can be done?
As an easy solution we purchased a Sekonic C-800 spectrometer. It can not only measure the light intensities but also their colors. Using this handy tool we can quickly measure all types of light emitters.
In the whole procedure and what we want to achieve one important part is how we capture things but there is the other part: how we recreate things. In this we are always limited by the render engines and their capabilities of what they can simulate. We did our first tests with Corona Renderer with which we are in luck, because most of the measurements we made can directly be used in the engine.
There are also different aspects of these light-sources which are captured, but currently not used in the 3D software due to limitations of what is possible.
There was one issue tho that we had to tackle when it comes to recreating these light-sources in our 3D programs: light meters only can measure how bright a surface would be at the distance where you hold the light meter, but they can’t define the intensity of the light itself.
If you would like to still have lumen as an input value to your light source, you need to do some math to get to the answer. The solution to the problem is the following: by definition one lumen equals to one lux on a square meter. An easy way to get the proper lumen value is to hold the light meter in a 28 cm distance from the light source. At this distance the virtual sphere around the light would have a surface area of one square meter, so you get the proper lumen value by measuring the brightness this way.
By averaging some measurements around the light source from the same distance it is easy to get the proper light output in lumen. The same can be done with lights that don’t equally distribute light in every direction, only the formula gets a bit more complicated.
With all this knowledge and when everything is done correctly, building up a library of scanned lights becomes fairly easy.