# 400 watt metal halide for exposing screens



## rockersuk (Feb 2, 2009)

would this 400 watt light be ok for exposing screens
400 Watt Metal Halide OR HPS Sodium Dual Hi-Bay Light | eBay UK

thanks


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## Alan Buffington (Oct 27, 2010)

rockersuk said:


> would this 400 watt light be ok for exposing screens
> 400 Watt Metal Halide OR HPS Sodium Dual Hi-Bay Light | eBay UK
> 
> thanks


You may get an image to show up on a screen, but in all honestly this is a flashlight compared to a real exposure lamp, ok for short run plastisol prints but you will need:

Exposure time: run a step test, create 10 2" panels with a magic marker on the bottom of your coated screen. Tape down a detailed positive really well. Block out 9 of the ten panels with rubylith, and expose the first panel for 2 minutes. Move rubylith or thin cardboard to the next line and expose again for another 2 minutes. Continue moving the block out material to the next line and expose for 2 minutes each time. When all ten 2 minute exposures are done you will have ten panels with the exposure times running from 2 to 20 minutes. Develop screen.
Pick out best exposed panel, no slime on the inside of the screen, all details from the positive wash out sharp.

If your 20 minute exposure panel still has 'slime ' on the inside of the screen during development with water the lamp is inadequate.

Alan Buffington
323-697-4334
Murakami Screen.com


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## PositiveDave (Dec 1, 2008)

Exposure is an additive process, so if you put out half the uv, you double the time. You can do it with this bulb, I don't know about it's output and how long it will take.


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## rockersuk (Feb 2, 2009)

Thanks for the replys.could anyone tell me what sort of metal halide light I would need and were to get them based in the uk


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## foot print (Jun 2, 2010)

Make sure you get a ballast that is rated for the MH bulb.. I build my exposure unit and use a 400w MH and expose screens in 1min 45 sec. They come out perfect and have printed hundreds of shirts without any issues. I am hoping to get a 1000w MH and then I can expose screens in 25 sec. Make sure you have a vacuum top it makes all the difference.


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## Alan Buffington (Oct 27, 2010)

Exposure time is shop specific. The age of the lamp, the output of the lamp, the humidity in the shop, the type of mesh, the thickness of the emulsion coat, the type of emulsion, the type of film, the dmax of the film, the distance of light to the screen all have a part in determining exposure time. I take tech calls to get our emulsion to perform. 

the key areas that need emphasis:
1. Just cause it is metal halide doesn't mean it has the right spectral output to expose emulsion. It could just be a bright white light with little UV and little strength. Just because you can create an image with a weak light source doesn't mean it is a 'production friendly' screen. Hand printers and DIyers can use these lamps and get results, but no where near the strength and quality of a 5kw system, or even the sun.

2. Standardizing coating technique and running a 'step test' for each mesh count as described previously is the only way to know what exposure time is needed.

If you take a white piece of cloth and wipe the inside of the screen away from the image area during development under water and you see emulsion color or what I call 'slime' or unexposed emulsion the screen is underexposed. With care you can wash it out carefully, use an air hose to keep open areas open. But you only have an image, not a fully exposed screen. Print quality will suffer, pin holing will be common, or breakdown with discharge, and if you are using an SBQ pure photopolymer emulsion it will be difficult to reclaim. Pre sensitized emulsions are SBQ based, they need to be exposed completely for best results in print and reclaim. Always run a step test to get maximum exposure. Underexposing your screens to get details just shows you need a better emulsion that can withstand complete exposures.

Alan Buffington
murakamiscreen.com


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## PositiveDave (Dec 1, 2008)

The glass on the light is probably uv protected (you don't usually want to expose people to uv (it doesn't cure them  )) Try removing it.


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## rockersuk (Feb 2, 2009)

thanks for all the replys much appreciated!at the moment im using a 500 watt halogen light but need something a bit better.
can anyone recommend a metal halide light for exposing screens or were to buy the right ones

cheers


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## Alan Buffington (Oct 27, 2010)

An excellent suggestion, I never thought about re-moving the protective glass cover. Has anyone else seen improved exposures with low wattage metal halide lamps with the safety glass removed?


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## Alan Buffington (Oct 27, 2010)

If price isn't an issue Amergraph 150, 3k, 7k, Olec 5kw or 8kw, Douthitt 3kw, 5kw, and Nu Arc Tri Light 6k are all good commercial grade exposure units. If price is an issue and you have strong sunlight you can expose quite well with the sun.


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## rockersuk (Feb 2, 2009)

price is an issue on a tight budget maybe try and pick up a used one but not came across any in the uk

cheers


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## bobbob1982 (Apr 7, 2008)

I live in the UK and use a 400w metal halide lamp. You can get them online if you just type in metal halide grow lamps, think people use them for growing hash and also for reptile tanks. You can also get it from this site silkscreenprintingmachines.co.uk. I bought mine from here it works very well. They give you a stupid vacum bag with it which is fxxxxxg useless but the bulbs great m8.


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## rockersuk (Feb 2, 2009)

was looking at that one from silkscreenprintingmachines.co.uk
is it good for doing halftones!i think its a 600 watt metal halide
but will have a look

cheers


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## PositiveDave (Dec 1, 2008)

If price is an issue, remember that the uv bulbs are very expensive and need replacing regularl.


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## rockersuk (Feb 2, 2009)

PositiveDave said:


> If price is an issue, remember that the uv bulbs are very expensive and need replacing regularl.



dave
how much are these bulbs say 400 watt and who sells them in the uk


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## PositiveDave (Dec 1, 2008)

try ADELCO WEBSITE | MANUFACTURERS AND SUPPLIERS OF WORLD CLASS PRINTING AND DRYING SYSTEMS SINCE 1972 or www.inksandmore.co.ukhttp://www.inksamdmore.co.uk


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## wthorpe (Aug 17, 2013)

What is or was the distance from your light to screen with the 400 watt Halide?


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