# Simulating light ray movement inside swimming pool water. Light sources not in the water

Dear list,

Hello my name is Sotiris Papantoniou MSc student of Welsh school of
architecture doing my dissertation in the field of lighting. I am trying to
identify if Radiance can simulate correctly the light ray movement within
the water. An actual swimming pool will be simulated and the data from
radiance will be compared to real time underwater light measurements. The
overall purpose is to identify if possible glare problems can be found with
the use of radiance before the actual construction of the swimming pool.

Reading all the previous mails about water I have found that dielectric
material is the most appropriate to use.

Apart from that mist pseudo-material has been suggested as well. Since my
light sources are not in the water but 3 or more meters above it, would you
suggest to create 2 mist volumes as it is described in RwR or avoid using
mist?

Any other suggestions are accepted since I am actually lost within all these
information

Sotiris Papantoniou
MSc Environmental Engineering
Cardiff
Mob: +44(0)7724711345

Hi and welcome,

you have choosen a difficult topic, as there are many unknown variables in what you want to simulate.

But first of all, what glare are you refering to? Glare caused by reflections, which could be experienced by someone next to the pool?

Water could be modeled purely as a dielectric. Mist would show the effects of bubbles, small particles, anything that makes the clear water become somehow misty So you would have to know whether the water in your pool is perfectly clear (e.g. a diver in it would not see a light beam when you point a strong spot to it), or whether you would expect any kind of particles in there (which would make that light beam become visible due to scattering). You may also use mist if there is mist in the air over your water surface due to condensation in the (compared to the water) colder air.

Second, what is the surface of the water body looking like? On earth, due to gravity, you would expect it to be almost perfectly plane, but experience tells us that there are small waves and such due to air movement, swimmers and such. Unfortunately, the surface geometry of a dielectric material has a huge influence on how you perceive it. So you would need to know the shape of the water surface in order to simulate it. If you go into this, the photon mapping extension may be valuable, as it can show caustics as you would see them under a wavy water surface on the ground of the pool.

Cheers, Lars.

Hi Sotiris,

You should search for the following:

water - any news???

at www.radiance-online.org. This will result in a thread discussion on the topic in which Greg Ward provides some suggestions and a script for using the "rtcontrib" tool in Radiance for doing simulations including water.

Regards,

-Jack de Valpine

Sotiris Papantoniou wrote:

···

Dear list,

Hello my name is Sotiris Papantoniou MSc student of Welsh school of
architecture doing my dissertation in the field of lighting. I am trying to
identify if Radiance can simulate correctly the light ray movement within
the water. An actual swimming pool will be simulated and the data from
radiance will be compared to real time underwater light measurements. The
overall purpose is to identify if possible glare problems can be found with
the use of radiance before the actual construction of the swimming pool.

Reading all the previous mails about water I have found that dielectric
material is the most appropriate to use.

Apart from that mist pseudo-material has been suggested as well. Since my
light sources are not in the water but 3 or more meters above it, would you
suggest to create 2 mist volumes as it is described in RwR or avoid using
mist?

Any other suggestions are accepted since I am actually lost within all these
information

Sotiris Papantoniou
MSc Environmental Engineering
Cardiff
Mob: +44(0)7724711345

_______________________________________________
[email protected]

--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

Hello again,

At first thank you for the welcome and the immediate answers.

Lars, my concern in the dissertation is the glare effect created in the
swimming pool and do not allow a lifeguard to search the bottom of the pool.
According to the theory found till now, I am interesting in the amount of
light reflecting from the surface and the amount that is travelling through
the water till it hits the bottom and all the way up. The ratio of the
intensities will show me how much glare I have in the swimming pool. I have
correctly the reflection of light and for this reason I am working for the
amount of light that travels in the water. Thank you for the information
about the dielectric and I think that I will abandon the mist
pseudo-material. Since water is clean in the swimming pool.

" but it seems like there are more mails than those I have found. I will
search them all and I'll try to understand the "rtcontrib" tool. I may come
back with any new questions.

Thank you all for your time

Sotiris

Hi!

Lars, my concern in the dissertation is the glare effect created in the swimming pool and do not allow a lifeguard to search the bottom of the pool. According to the theory found till now, I am interesting in the amount of light reflecting from the surface and the amount that is travelling through the water till it hits the bottom and all the way up. The ratio of the intensities will show me how much glare I have in the swimming pool.

Wow, this sounds like a not so trivial problem... I think you need first to study on what surface shapes to expect. On a perfectly even surface, you could easily look through to the ground, as long as you do not hit the total reflection by very low angles. But as the lifeguard will usually be interested in the pool when there are occupants, the surface will not be a plane any more, but wavy. And now everything depends on the shape - having big, smooth waves will allow good view, but small wrinkly waves (ok, here I hit the limits of my English language skills) would cause a lot of reflections by total reflection, and at the same time caustics resulting in uneven illuminances on the ground. If you are able to model the water surface geometries which you need to consider, it will be possible to make some estimates on visibility of anything below the surface. There are two ways afaik, one being rtcontrib, the other one pmap. rtcontrib comes with recent distributions, but is not really documented. pmap comes with a nice documentation, but is currently supported only with radiance 3.7.

By the way, I think there are two effects to consider. One is glare. Even more important may be the total-reflection that simply does not permit you to look through a water-air interface (aka the water surface) under narrow angles, with or without glare. Glare alone might render the task of the lifeguard tiring, but non-visibility renders it impossible...

Cheers, Lars.