Lighting gel / filter / diffuser ?

[Adrian]

Hi

Any theatre / disco lighting experts out there ? One of my new stained glass products is a lamp, with a wooden base, and the 'shade' shaped like a 'Toblerone' bar standing on end.

Inside the shade is a compact fluorescent lamp (let's not have that discussion again ! ) - and the shade consists of various pieces of stained glass, fused glass, polished agate slabs etc...

The CF lamp is used because the finished lamp is not all that large, and a conventional tungsten lamp would give out too much heat.

Only problem is - wih certain types of stained / art glass, it's sometimes possible to see the outline of the lamp bulb, or of the plastic body of the CF lamp - which detracts a little from the overall effect.

So - bright idea time

How about using a piece of rolled up translucent material between the CF lamp and the 'shade' - just to soften the outline of the bulb a little....

I vaguely remember, from my college days running theatre / disco lighting, that we had (?)acetate sheets called 'gels', that were used in front of flood / spot lights. I see that these are still available

- I'm guessing that a 'neutral density' one is the way to go...

Alternatively, I see this item

wonder whether this would do the trick. Never seen it before - has anybody used it and can tell me if it is as rigid as 'real' gel ? Looks like it might just be 'fabric' - in which case it wouldn't stay put inside the lamp.

Alternatively - does anybody have a suggestion for a readily-available, durable, safe material that I could use instead ?

Many thanks in advance Adrian

[Rod]

Adrian,

As I recall (and it was a long time ago) the neutral density gel was to allow the effective brightness to be reduced without using a dimmer (and the consequent colour shifts of running lamps at different filament temperatures) or any form of aperture control.

In a vaguely similar way, ND filters can be used photographically to allow a larger aperture/longer exposure to be used when required. It certainly does not act as a diffuser in this role!

The linked product looks to be appropriate (but I don't have the experience to judge - just 'makes sense' level).

[Adrian]

HI Rod

Thanks for the reply..

Ah - probably not one of those then

No - I suppose it wouldn't ......

You're in the same boat as me then... perhaps there's an expert about ?

Thanks Adrian

[John]

When I did stage lighting you could get various degrees of "Frost" gels

[Peter Parry]

Use an acrylic tube of diameter suitable to fit over the lamp and leave a bit of room for air circulation and cut to length so it covers the bulb completely.

eg

upon quantities you intend to make either buy translucent rather than clear tube or make it translucent by getting a cylinder hone such as

running it up and down inside the tube until you get the desired effect (Cylinder hones are flexible devices used on a normal electric drill which have 3 abrasive pads designed to prepare the surfaces of things like engine or brake cylinders -they produce a fine series of scratches which if used in plastic tubes gives it a translucent surface a bit like rubbing it with sandpaper).

[Adam Aglionby]

Diffusion gels are available in quite a range, spun isn`t probably what your looking for it softens the glare from big light sources at a distance.Frost is a slightly smaller sledgehammer for same purpose.

To reverse the linear look , a Silk is possibly what you want, this, clear, gel is brushed in one direction so might mitigate the vertical linearity with a tube of horizontal orientated silk. In extreme cases silk horizontal and vertical but lose a fair amount of light.

in yellow pages for local theatrical lighting trade counter, they`ll stock one or both of the above 2 ranges, have flick through their swatch books, gel isnt expensive.

HTH Adam

[Adam Aglionby]

Addendum

usenet sci.engr.lighting and rec.arts.theatre.stagecraft could do with the traffic if you have similar questions :-)

[Thomas Prufer]

Fiberglass, as used in auto body repairs? Comes in woven and non-woven (felt-like, mat, I forget the term...), it's heat resistant, and could be firmed up with epoxy. too...

Thomas Prufer

[Adrian]

HI Peter

Thanks for the reply

That's a possibility. Seems a bit 'overkill' though - and possibly tricky to transport in 2m lengths (we live in the back of beyond out here in South-west Ireland).

I was thinking that sheet gel might work out cheaper on the postage...

It's a possibility though - thanks

Adrian

[Adrian]

HI Adam

Thanks for the reply

what results...

Thanks again Adrian

[Adrian]

A possibility - but maybe a bit 'user-unfriendly' (if it's the stuff I'm thinking of it sheds fibres rather easily)

I was hoping for something that I could just slip into position, if you know what I mean !

Thanks Adrian

[gilli]

Hi, I would go to

where you should get good advice. They should have all the diffusers and gels you need...the diffusers come in different types and densities...degrees of light reduction...or you could get clear in different densities... They are made to withstand very high heat so you could put them as close to the bulb as you like just staple into a tube as a test and drop it over...they handle both rosco and lee. I suppose you could glue into a tube shape for more permanent job. They will give you a sample book of both makers so you can experiment and choose. I have some on hand which I would post if you like...not sure how much or which ones...don't use them anymore. You might have to buy a whole roll if you want the diffuser....best to check first...the gels they will do in smaller sheets, but, from memory, the diffusers only come in rolls...ring to check first. David G

[Dave Plowman (News)]

To soften a point source you use stuff called 'spun'. ND is used to reduce intensity without altering colour temperature or on a light that can't be dimmed.

[Peter Parry]

Tracing paper - even cheaper (or baking paper - similar but temperature resistant).

[Adrian]

Hmm - would it last, though ??

Adrian

[Adrian]

Ah - OK I got an email back from Lee Filters - they seem to think that I need

"a 129 Heavy Frost or 216 white diiffusion".

and then went on to comment

"216 transmits 36% light while the 129 is darker with a 25% transmission".

But they've also given me a contact in Dublin who is both a stockist and a 'user' of their products - so hopefully I can get some sheets of various materials to play with and decide which one's best...

Many thanks Adrian

[Peter Parry]

Probably as well as a film, and much easier for the user to replace if/when it gets damaged.

's a silicone coated paper stable up to 230deg C or so. Bakewell is one commonly available brand name.

[Dave Plowman (News)]

Yes - those would do but IMHO more likely to show through the glass as a bit of a bodge. They are a form of thin sheet plastic. 'Spun' or 'silk' could be made into a sort of bag which would look better.

Do you have location filming going on in your area? If so ask the sparks for some offcuts. It's normally used in pretty large pieces to cover windows etc so has a fair amount of wastage.

[Adrian]

OK - understood..... Would 'bagging' a CFL be a bad idea from the heat generation / unit life point of view ?

Not that I know of..... Not a lot of call for gloomy West Cork weather in filmed drama at the moment - or so it seems

I'll keep my eyes peeled....

Many thanks Adrian

[meow2222]

Paper liners work well in terms of distributing the light, but even thin ones reduce light throughput quite heavily.

Gels are unnecessarily expensive.

A plastic tube around the lamp would likely be unsafe if someone installed a filament bulb. Also a best it could only enlarge the visible light source to the size of the tube.

One most effective diffuser material is woven nylon cloth. This effectively conceals the light source. It can be used as a shade liner, and is then compatible with all lamp types. I dont know the light transmission figure, but not far off 100%.

Yes. It could also be dangerous if you combine this with normal end user practices.

NT