Actual failure mode of Gel

[Ekij]

I’ve read a lot of past posts about Gel ‘burning’ out but I’d like to know exactly what the failure mode is. I’ve more experience with sound than lighting and know that when speakers ‘explode’ they don’t literally explode.

 

As I only get to do lighting occasionally ;) I am tempted to invest in E-colour rather than Roscoe or Lee as I can get twice the amount for the same price but I am worried about what will happen when it fails. I am doing lighting in someone else’s venue and have no idea what the power of the lighting will be until the night. Nor do I know what size of Gel holders I need! ;)

 

If the E-colour ‘burns out’ I don’t want bits of molten plastic dripping onto the people below, nor do I want to set fire to the front of the light. If it simply ‘loses’ its colour I can live with this.

[peter]

Certainly with Lee filters, when the gel burns out, it simply looses its colour and becomes 'crispy'. Eventually a hole will appear in the centre of the gel, but this generally takes time (except with Lee 181 on a spotted down Fresnel ;)).

 

Sometimes gels can smell like they're burning when first placed into a fixture, but this is due to an oily residue from the manufacturing process and should wear off quickly.

[Modge]

Blue's in my experience (esp lighter ones) fairly quickly gain a lighter circle the same shape as the light they are in front of (esp in a venue light ours where a large proportion of the lights we use have to be 1KW parcans owing to lack of cash). This means they're no longer really the colour they should be. 1/2 white diffusion is possibly the worst for melting actually - I've had it before where it melts it self to which ever other gels it's sandwhiched in with and needs peeling apart.

[the kid]

We had some HT red I think it was plasa that developed a "drip" it did not drip as such but I think that given enough time it might of done. I was told to chuck it to day, I knew I should of posted a pic of it.

 

To protect you can use heat shield in front of the gell ( lamp - lense - heat shield - gell) but you will need 2 colour frames to let air circulate between the two.

[peter]

Or you could use a pizza cutter (someone's posted the correct name, but I forget) to place some tiny perferations in the gel to imrpove air circulation.

[kalmatthew]

Not a pizza cutter, ;) that would cut through the gel, a dress makers marker wheal (ponce wheal)

[Stu]

To protect you can use heat shield in front of the gell ( lamp - lense - heat shield - gell) but you will need 2 colour frames to let air circulate between the two.

As an addition to this, I've found it really depends on what lantern your using to how succesfully you can use heat shield and gel together in two frames. SLs are OK because there is quite a gap between the 2 colour frames when installed, but I found once with S4s that the frames got too close together, and the colour and heat shield met and melted together into one big blob.

 

Don't even get me started on Alto's!

 

In addition to the OP's question, you'll find Rosco colour normally lasts longer than Lee - all in the manufacturing process. I don't know the physics behind it but it does. You'll also find the same thing happens with GAM or Apollo gel. Lee have a HT (High Temperature) range which does help the situation. Not every Lee colour is in the HT series, but it should be marked in the swatch book or on the website.

 

A bit of physics I do know is that gel works by blocking out the bits of the colour spectrum which isn't required to make that colour. Can't think of an easy way to describe it but basically whatever part of the colour spectrum is blocked out, the gel absorbs. Each gel has a transmission rate - this means how much light you'll get out of the gel. So for instance, L181 Congo Blue is about 0.8%. So if you put this in your lantern, you'll only get 0.8% of the light out of the otherside. And because gel absorbs it, all that light and therefore heat helps to melt it, destroy the colour etc etc etc. Not the best physics lesson I could give but it hopefully illustrates a point.

 

As an aside, dichroic colours (as found in Moving Lights) reflects the light...

 

Also, all modern gels are now fire proof so they won't catch alight at the front of your lanterns. I believe this is why you can't get Strand Cinamoid these days - as a complete aside.

 

HTH

Stu

[robloxley]

Eventually a hole will appear in the centre of the gel, but this generally takes time (except with Lee 181 on a spotted down Fresnel ;))

Also with certain profiles if you focus them with the beam 'crossing point' at the same distance as the gel frame you can punch a hole in Lee 119 in less than 10 seconds!