Dichroic Filters!!

[dblight]

Hi!

 

I'm currently working on a lecture demonstation next week about dichroic filters! I was wondering if anyone has any useful information for me about how I could go about demonstating this?

I was also wondering what people think of them and whether there is a future for them within the lighting industry?

 

Thanks for your help ;)

 

Dani!!

[tokm]

I was wondering if anyone has any useful information for me about how I could go about demonstrating this?

Stick one or more in front of a light source to demonstrate colour mixing.. Do some research into how they work and explain.. give examples of what they're used in..

 

is a future for them within the lighting industry?

I expect so.. Most moving lights use them in some way or another, mostly as part of a colour mixing system or on a colour wheel..

 

HTH, T

[Guest lightnix]

Hi Dani, welcome to the Blue Room :(

 

The best way to demonstrate them might be with a... live demonstration! How they work, compared to dyed filters (e.g. gel) is a pretty simple concept to understand; your greatest challenge IMO, will be making the demo any longer than the 2 minutes it'll take to explain ;)

 

We all love dichroics - they revolutionised the lighting industry, by being heat resistant enough to put inside luminaires and giving us all those sumptuous, saturated shades to drool over!

 

Have they got a future? Well the moving light manufacturers seem to think so; dichroics having been the filter of choice, since movers first properly appeared, almost 30 years ago ;)

 

Maybe you can get some samples from one of the moving light manufacturers, or from a company like this one.

 

Good luck - please let us know how it went.

[adam2]

As others state, dichroic colour filters are in general use in moving lights and other colour changing devices.

 

They are seldom used as a replacement for gels in traditional lanterns though for several reasons

 

1) Very expensive, especialy in the large sizes needed for most lanterns. (the relatively small dichroic filters in movers are cheaper, and a small proportion of the price of a relatively costly article)

 

2) Fragile, again not a concern in a mover since the filters are built into a robust housing, but not very suitable for use in regular lanterns

 

3) The light colour varies a great deal depending on at what angle the light passes through the filter.

A wide beam light will have different colours in the middle of the beam and at the edge.

 

I have installed dichroic filters on fixed archtitectural lights very succesfully, but in view of the price and risk of breakage would not recomend them for most theatre uses.

Possibly worth considering on long running shows though since they dont fade or burn through.

[JackPott]

Would definitely try to get hold of one you can pass round. I have dichroics for all my video lights and spent more time than I probably should admit to looking at them when I first got them.

 

If you look at them the surface appears orange, but if you look through them everything turns blue! Magic! ;)

[dizzidido4]

hows bout doing the history of them as they may help you 'predict' their future. We need to see where we've come from to know where we're going good luck

[Kelite]

And be sure to change the angle at which the light passes through the filter, causing the color to shift. This color shift can be described to non-theater types in a simple fashion, comparing the setting (or rising) sun that projects through a much more dense portion of the atmosphere. As you know, the thin film is thinnest when light passes at a 90* angle, but the light must penetrate mor coating when at an angle.

(My kids understand it now that I've explained it to them in this way-)

 

Good luck with your presentation!

[musht]

If you want to get into the how:

 

http://dev.physicslab.org/Document.aspx?do...nterference.xml

 

but think liked Keith`s explanation better ;-)

 

History have heard was thin film coating on optics comes from astronomy and to lighting via laser mirrors. V*L were very quiet about their ingredient X in the early days.

 

Their weird property is they can be made as a very narrow band pass or notch filter as required, one of astro uses was 589nm notch taking out low pressure sodium streetlight glow.

[springgrove]

If you want to get into the how:

 

http://dev.physicslab.org/Document.aspx?do...nterference.xml

 

but think liked Keith`s explanation better ;-)

 

But Keith is describing a totally different effect.

 

Dichroic filters rely on interference of light, rather than absorption, as in gel filters or the atmosphere at sunset.

 

When light hits something it can be transmitted, reflected or absorbed. Dichroic filters do not heat up as much because they reflect the colours they do not transmit (very little absorption) hence the different (complementary) colour when you look at them.

 

When you change the angle, you are changing the path difference between the surfaces of the filter, therefore the wavelength of the light which is affected.

 

The OP probably needs to think whether he wants to describe their properties and uses (probably) or how they work (probably not!)

 

Nigel

[Tomo]

Keith's explanation is what I call "Lies to children"

It's not totally accurate, but it's reasonably close to the truth.

 

Nigel:

Absorption is how gels work, but it's not why the sky is blue or the sunset is red.

The blue sky and red sunset are in fact due to "Rayleigh Scattering", which is very similar to the thin-layer destructive interference that dichroic colours use, except that it isn't the same at all.

 

But it's close enough to help you visualise the overall effect.