T5/T8 model for LightTools

[Frank Knappe]

Hello,

at the moment I'm evaluating LightTools for doing the necessary
simulation tasks in our company. Unfortunately the source models ORA
provide are mainly LEDs and lamps for automotive applications. They
don't have a model for T5/T8 lamps. While you can easily model them as
cylindric surface emitters, this doesn't take into account absorption
effects if light from a mirror is back reflected into the cylinder. I
contacted Philips and OSRAM for support, but the people in question
are/were on holiday.

Does anyone have a more detailed optical model for such fluorescent
lamps? Or the basic idea, how to model (quantitative) the absorption?

Thanks in advance.

 

[Frank Knappe]

We are a german company, delivering such kind of photometric services.
We can supply the necessary ray set data (Strahlendaten) of any kind of
lamps, luminaires, LED or many other light and radiation sorces You
need, as we measure them for many lighting corporations in Germany and
Europe (also for OSRAM). If You rather ask OEC in Munchen, they know
obout this possibility in Ilmenau.

I might be wrong, but I don't think that measured ray data will help me
here. From what I understand, the ray data give you an exact model of
how the light emits from a certain source, taking into account all
possible external surrounding materials. If you cange this surrounding,
you have to measure again. For my task this would mean that you would
have to measure any combination of light source and reflector. Lots of
tests. And in principle I want to simulate so that I don't have to do
such measurements.

 

[Frank Knappe]

For most illumination design tasks like this I usually start with what
is called a ray distribution model, this is a measured model of the
light source that takes into account all of the fabrication errors and
optical properties of the lamp that most lamp mfg do not know of if
they do know it they cant disclose.
so the industry has developed ray distribution models of the sources,
you can usually download these from the source mfg website.

For this kind of description model I'm not sure it it is applicable if
light is back-reflected into the source.

If you want to create a model from scratch then you will use the
feature in the illumiation design software.
For example as you say you will create a hollow cylinder glass
envelope and also use a cylinder source and create the mirror behind
the source.

That's the way I do me test simulations right now.

In most of the illumination design programs like light tools (such as
zemax, fred, asap, tracepro) you can set the optical properties (like
absorption, index, scatter, coatings) for each object or optical
surface. So for your absorption you can input the absorption in the
glass and other elements like condensers and get a decent model of the
signal at your detector.

The problem here lies in the quantitative description. Here I was hoping
that someone else already has done such work in the past. For me the
only way would be the fitting of certain parameters to measured light
distribition curves. All the glass values are maybe known, but I wasn't
aable to find information about the gas itself and the used phosphor.

 

[Frank Knappe]

You might try Mark Jongewaard at LTI optics as he has has modeled
fluorescent tube properties for his software (Photopia), although I
don't know how willing he would be to share to help with a competitors
software. He might be willing to do the measurements of the pass
through properties you need for a fee though.

I will wait until we have our decision, which program we will buy.
Unfortunately every program has it's disadvantages. It's like looking
for the smallest amount of pain.