# DIY Exposure Unit Halogen vs. Metal Halide



## kylerogers (Jul 30, 2008)

I'm planning to make a better exposure unit. I called a local hydroponics shop and they did jave the metal halide bulbs with the sockets and ballasts and everything.

I'm wondering if using a halogen wouldn't be a heck of a lot easier. I'm using a Lawson Quest right now, which uses a 500 W Halogen.

I looked at the Lowes website and they have a 800 W Halogen Work Light for $25.00. (There was also a guy on this forum that made one uses two 500Ws that looked quite well made).

I looked at a 1000 Watt Metal Halide bulb on an online hydroponics store and it was $300 for the bulb, socket, and ballast!

Plus the $5,000+ exposure units that use metal halides use their own bulbs and ballasts that are designed to come on instantly. From what I understand, the commercial bulbs and ballasts have to warm up. These means making some sort of shutter for the bulb while it's warming up.

Seems like it would be a heck of a lot easier and cheaper to go with an 800 W halogen or two 500 W


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## out da box (May 1, 2007)

The difference between the 250.00 halogen vs. metal-halide is well worth it. I paid 150.00 for my 400w metal-halide light and ballast and it kicks butt. You do have to warm up-5 minutes- and you need a shutter. 
But... I burn in seconds, not 8-20 minutes and I burn very, very sharp halftones.
Get the metal-halide whatever the cost.
Never go cheap with screen printing, too many things can go wrong.


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## tdigital (Sep 14, 2008)

Agreed! Time is money. Kyle are you close to central florida? I have a guy who has 4 1,000W lights+ballasts left for $75 ea..


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## kylerogers (Jul 30, 2008)

I may just start by getting the glass and building a frame. I have two 500 w halogens as it, or I may get this 800 w one. Later on I can upgrade with a metal halide and then a vacuum blanket.

Right now I have a Lawson Quest, which is a 500 watt halogen about 16" or so above the frame. You just lay a small piece of glass on the frame. I made a piece of black covered foam to go underneath the frame, but it is far from ideal. Also, the frame for the halogen is junky and does not even point straight down, it points at an angle.

It had been working good for a while, but I was just doing really simple stuff. As I've increased the detail of my designs, I've been having more and more problems with emulsion not washing out. 

This is what R Jennings says in his building your own exposure unit video. He says it needs to be 21" or more. He says that at 21" expect a 500 w halogen to take 30 minutes, but doubling the wattage to 1,000 reduces the exposure time by a factor of ten. So a 1,000 W Halogen at 21" would exposure the same screen in 3 minutes.


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## kylerogers (Jul 30, 2008)

tdigital said:


> Agreed! Time is money. Kyle are you close to central florida? I have a guy who has 4 1,000W lights+ballasts left for $75 ea..


I'm planning to attend the ISS show in Orlando in February.


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## tdigital (Sep 14, 2008)

good deal! I'll more than likely run into you there. Good luck with that exposure unit. I have some pics of mine posted here in another thread if you wanna take a look. I built a vacuum lid and its SICK! I'm finishing up my drying cabinet and i'll have pics up by saturday.


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## kylerogers (Jul 30, 2008)

Is this the one. http://www.t-shirtforums.com/screen-printing/t70769.html

I saw your pics a few days ago, the unit looks awesome. Probably the nicest homemade one I've seen so far. Do you have a hose going through the pond liner for the vacuum suction?

I plan to make screen drying cabinet for myself also. I use a dehumidifier now. I coat the screens in a small room with dehumidifier. Then when I go to burn a screen, I put the other screens in a black garbage bag and move them to another room. So far the garbage bag has actually worked.



tdigital said:


> good deal! I'll more than likely run into you there. Good luck with that exposure unit. I have some pics of mine posted here in another thread if you wanna take a look. I built a vacuum lid and its SICK! I'm finishing up my drying cabinet and i'll have pics up by saturday.


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## tdigital (Sep 14, 2008)

kylerogers said:


> Is this the one. http://www.t-shirtforums.com/screen-printing/t70769.html
> 
> I saw your pics a few days ago, the unit looks awesome. Probably the nicest homemade one I've seen so far. Do you have a hose going through the pond liner for the vacuum suction?
> 
> I plan to make screen drying cabinet for myself also. I use a dehumidifier now. I coat the screens in a small room with dehumidifier. Then when I go to burn a screen, I put the other screens in a black garbage bag and move them to another room. So far the garbage bag has actually worked.


Yes, that's the one, thanks! The hose is actually going through the lid, see the attached pic. How long would you estimate it takes you to dry 4 screens with your dehumidifier? I can't wait to finish this thing!


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## kylerogers (Jul 30, 2008)

Ok, I see the hose. I think I see what is going on. You have the hose in between the blanket and the glass.

Basically, with the dehumidifier I give it 30 minutes just to be on the safe side. They are always bone dry before the 30 minutes is up. It doesn't matter how many screens I do at once. I have the screens in a small room, and basically the dehumidifier essentially turns the whole room into a drying cabinet.

The unit I have blows out the dry air out the top. So my idea is to build a cabinet where my dehumidifier would be in the bottom half and the top half would have racks with sides and a top to shield it from light.

When I took the screen printing class from Lawson, they told us that a good dehumidifier in a small room with the screens will actually dry them faster than a commercial screen drying cabinet which just uses hot air.

When I first started burning screens last August the humidity was really high and it was taking 8 hours or more for my screens to dry.

I first tried to go cheap and bought a $50 dehumidifier from amazon.com. It was completely totally worthless. After running it for three days straight it barely collected any water and I sent it back for a refund. I then got a small unit at Lowes for $150 that works great. 






tdigital said:


> Yes, that's the one, thanks! The hose is actually going through the lid, see the attached pic. How long would you estimate it takes you to dry 4 screens with your dehumidifier? I can't wait to finish this thing!


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## kylerogers (Jul 30, 2008)

Here is something I found online. These designed for exposing screens to big for regular exposure units. They make them with the stands also, but one without the stand would be perfect for a homemade metal halide exposure unit.

I don't know how much these are but it's a metal halide light fixture with a mechanical shutter and a precision timer. Their website says the timers are in .1 seconds. 

Their bulbs are supposed to be specifically for exposing Diazo and Photopolymer. 

Apparently it has a low, medium, and high settings that range from 1,000 watts to 2,300 watts. However, several companies sell the bulbs online and they charge $250. So I'm sure the whole unit is really outrageous. Your paying a fortune to have different wattages in the same unit.

I think the purpose of having different wattages is because you are supposed to have the light source further away depending on how big the screen is. So with this, you would be able to place it at three different distances for three different sized screens, but it would take roughly the same amount of time for all three.

It would be nice if they made a simple low cost 1,000 watt version.


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## sink (Jun 20, 2007)

I bought a used ballast, and new metal halide bulb. 
total $250 from a hydroponics shop

I expose my screens depending on mesh, 20-40 seconds... it is the only way to go, I cant imagine waiting minutes...


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## out da box (May 1, 2007)

You got that right, I cant imagine waiting minutes either. Used to do them in 10-20 sec.


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## BroJames (Jul 8, 2008)

out da box said:


> You got that right, I cant imagine waiting minutes either. *Used to do them in 10-20 sec*.


Ridgely, "used to"? I think I read somewhere that your bulb to glass distance is 24"? What is the size of your glass what is the largest image you have burned with your MH unit?

Do you use a pressure washer to wash out the emulsion? Or just household water pressure?


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## out da box (May 1, 2007)

My glass is 32x40. I burn 23x31 screens 17"x 22" is the biggest image I burned. I just got a new 400watt bulb. Burn time with sbq is 30 sec. Dual cure is 2:30.


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## abchung (Jul 16, 2009)

I use a halogen 1000W, and use weight to press down the film.
I want to know which one is more important to produce sharper half tone images.
Metal Halide or vacuum blanket.

Please pick 1 due to budget restriction.


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## BroJames (Jul 8, 2008)

abchung said:


> I use a halogen 1000W, and use weight to press down the film.
> I want to know which one is more important to produce sharper half tone images.
> Metal Halide or vacuum blanket.
> 
> Please pick 1 due to budget restriction.


I would say the metal halide is more important. Lots of people have good results with weights on top of the mesh in lieu of a vacuum. I believed sir Ridgely used blocks to weigh down on the screen when his vacuum system broke down and had good results with the blocks.


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## abchung (Jul 16, 2009)

Thanks heaps BroJames. I needed that advice.


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## dominik (Jul 25, 2010)

i'm new to the forum but by reading up on others post i had my cousin build me an exposure unit,just curious if any one had any ideas to improve my diy unit.Oh, the dimensions are 26x33x38 light is approximately 23 inches from glass, 400mh light. sorry probably should have been first thanx to the whole community for all the knowledge and information i have gathered so far and special thanx to all the diy unit builders!!!!


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## BroJames (Jul 8, 2008)

dominik said:


> i'm new to the forum but by reading up on others post i had my cousin build me an exposure unit,just curious if any one had any ideas to improve my diy unit.Oh, the dimensions are 26x33x38 light is approximately 23 inches from glass, 400mh light. sorry probably should have been first thanx to the whole community for all the knowledge and information i have gathered so far and special thanx to all the diy unit builders!!!!


Well, its still a new post and you can copy the last paragraph and paste it at the beginning.

OK, just joking. Why not post a picture so we can see if we have any "improvement ideas"? And welcome!


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## armando03 (Oct 2, 2011)

how can i build a exposure unit using 2 500watt work lights how big should i make my box


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## BroJames (Jul 8, 2008)

An 18" high box with a glass about 18 x 24" should be good enough. You can actually lower the distance to 12" if you will be using 2 lamps but I expose at 18-24" when I was still using halogen lamps. Have you considered a single 1000w halogen or other UV sources?

You can also make a 30-40" high box and make the lamp's height adjustable. A 30-40" height box will enable you to switch smoothly to a metal halide unit in the future.


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## genteunidamx (Oct 27, 2011)

I live in Mexico and at electronics shop here I found a 1000w-1500w light for cheap. I use it, takes about 10 minutes to expose a screen. Its one very long bulb, the lights are used here for parking lots and large areas, its an outdoor light gets very hot.


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## ScreenFoo (Aug 9, 2011)

kylerogers said:


> This is what R Jennings says in his building your own exposure unit video. He says it needs to be 21" or more. He says that at 21" expect a 500 w halogen to take 30 minutes, but doubling the wattage to 1,000 reduces the exposure time by a factor of ten. So a 1,000 W Halogen at 21" would exposure the same screen in 3 minutes.


So this is a pretty old thread, but this really caught my eye. Does anyone have this vid? Did R Jennings really say this?


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## BroJames (Jul 8, 2008)

genteunidamx said:


> I live in Mexico and at electronics shop here I found a 1000w-1500w light for cheap. I use it, takes about 10 minutes to expose a screen. Its one very long bulb, the lights are used here for parking lots and large areas, its an outdoor light gets very hot.


Most likely a metal halide lamp


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## Naptime (May 19, 2011)

ScreenFoo said:


> So this is a pretty old thread, but this really caught my eye. Does anyone have this vid? Did R Jennings really say this?


yeah, it's been around a while .

[media]http://www.youtube.com/watch?v=x9NrndxeCJ4[/media]


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## genteunidamx (Oct 27, 2011)

BroJames said:


> Most likely a metal halide lamp


Hey, this is what I have, found these images online. Mine is exactly the same as this. I payed about 100 dollars for this. Works great.
peace.


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## genteunidamx (Oct 27, 2011)

genteunidamx said:


> Hey, this is what I have, found these images online. Mine is exactly the same as this. I payed about 100 dollars for this. Works great.
> peace.











Sorry about the image.


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## BroJames (Jul 8, 2008)

genteunidamx said:


> Sorry about the image.


That's halogen


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## genteunidamx (Oct 27, 2011)

BroJames said:


> That's halogen


Yeah it works its 220v, I haven't even seen the r jennings video, I just seen it, I built a little table just like that with a little timer on my switchbox jaja. Cool video.
peace.


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## BroJames (Jul 8, 2008)

I used to use a 500w halogen and then a 1500w halogen before switching to a 250w mercury then a 400w mercury. I use an industrial metal halide now. They all work.


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## genteunidamx (Oct 27, 2011)

BroJames said:


> I used to use a 500w halogen and then a 1500w halogen before switching to a 250w mercury then a 400w mercury. I use an industrial metal halide now. They all work.


Would this be something that works also? Planet Natural-- Checkout Step #1


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## BroJames (Jul 8, 2008)

genteunidamx said:


> Would this be something that works also? Planet Natural-- Checkout Step #1





> Order Processing: Step 1 of 5
> *Note:* We utilize advanced fraud detection software. If your billing information does not match your credit card information your order will be placed on hold until all information is verified.


Sure it works but in another thread and forum


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## genteunidamx (Oct 27, 2011)

BroJames said:


> Sure it works but in another thread and forum


sorry about that, I meant to put this link Agrosun Gold Metal Halide Bulbs


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## BroJames (Jul 8, 2008)

> hese spectrally enhanced halide bulbs are the best all-purpose growth and fruiting/flowering light you can use. They emit more of the red wavelengths than the common halides. They are the “Gold Standard” in plant growth lighting, and thousands are in use by satisfied gardeners worldwide


I'd bet that they would just as regular household fluorescent could expose. Most if not all lights emit photo-sensitive UVs in varying degrees which is lights in general is not good for emulsion. It exposes them in varying amount of time. The linked halide emits more red wavelength but does not say anything about the wavelength needed for exposing emulsion. Still, it is a metal halide "grow" lamp and I am guessing that it still exposes faster than halogens in the same watt range.


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## ScreenFoo (Aug 9, 2011)

I would absolutely love to know why Roger stated that 500 watts will burn a screen in 30 minutes and 1000 watts will burn a screen in 3.



Got some pretty funky light theory going on there...

Angel: What kind of differences did you see in burn times between your halogens, mercury, and MH?

I'm working on a *large* vacuum frame right now, figuring on going to a MH light source...


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## BroJames (Jul 8, 2008)

Except as noted, these are my personal exposure times using mostly SQB emulsion. I tried dual cure emulsion at about the same time I was using mercury. I also reduce or increase exposure times a little as I think necessary but the figures below should still represent a good average time. But note that they're under exposures. Proper exposure should take about twice to thrice as much time or more.

5 - 6 min, 24" distance, 500w halogen 
2:30 min, 1000w halogen (as posted by a colleague in this forum)
1:45 min, 30" distance, 1500w halogen 
1:45 min, 24" distance, 250w mercury (with 5 min warm up). I think almost 5 min without warm up.
1:15-1:30 min, 30" distance, 500w mercury (Used this only for a while)
1:30 min+, 30" distance, 400w halide (5 min warmup). Denser transparencies.

My 3x the wattage and 1/3 the time does not support the 2X wattage 1/10th the time statement attributed to Jennings. The experience of a colleague as posted in this forum states that his exposure time with his 1000w halogen (2X the wattage of a 500w resulted in 1/2 the exposure time based on the experience of others). This is more in line with my experience.

A colleague reported that the light/UV from mercury lamps fluctuates but I did not notice this. Probably because I do my exposures and printing during dawn where the electrical load is less and the current more consistent.


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## stevem98 (Mar 2, 2006)

metal halide 100%, we burn screens in 30 seconds, always the same and perfect


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## BroJames (Jul 8, 2008)

Is that DIY or commercial? What is the distance and wattage?


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## ScreenFoo (Aug 9, 2011)

Hey now, anyone who says their screens always come out perfect isn't being picky enough... 

I was quite intrigued in the respect that Kiwo, Ulano, and Saati over the years have put out a number of technical publications that outline more light and exposure theory than most printers will ever use, but the point being, at least theoretically, if you want to cut your burn time in half, you have to quadruple your UV output.

At the same time, I'd suppose it's quite possible there is proportionally more UV output as wattage increases...

Where's a UV spectrophotometer when you need one?


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## BroJames (Jul 8, 2008)

Quadruple the time if you double the distance with the same wattage is theoretically sound. Never tried it though. Double the wattage and half the time(or something close to it) does seem to be the case. I don't know what the theory is but I'd dispute the "*2X the wattage 1/10th the exposure time*".


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## giewtwo (Mar 1, 2012)

stevem98 said:


> metal halide 100%, we burn screens in 30 seconds, always the same and perfect


Question. What type of metal halide bulb is it? Is it specifically UVA bulb in between 350-20 nanometers or is it a standard full spectrum bulb?


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## selanac (Jan 8, 2007)

I took a Ryonet PVC pipe exposure unit and reduced the time to 3 minutes. Their recommendatin was 13 minutes, 16 inches from the top of the screen, 1/8 inch glass on top of the film. 

We cut the vertical pipes so we have 12" from the top of the screen. 1/4 inch Low Green Glass. New exposure time is 3 minutes, and the images comes out 50% better. Takes half the time to wash out too. 

Oh, Low green cost me about $80.00.


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## terrydolin (Mar 31, 2008)

BroJames said:


> 5 - 6 min, 24" distance, 500w halogen
> 2:30 min, 1000w halogen (as posted by a colleague in this forum)
> 1:45 min, 30" distance, 1500w halogen
> 1:45 min, 24" distance, 250w mercury (with 5 min warm up). I think almost 5 min without warm up.
> ...


So I was doing research and came across this, wanted to ask about the under cutting, we have a diy unit with 4 - 500 watt halogen bulbs in their alum case with the glass removed spaced about 1 inch apart, about 21 inch to the glass, we use a time of 3:30 min and on occasion we have a area on the edge that will be a bad exposure and not was out right, most of the time they are great, we use pc701 only because we get good results, but the question is should the bulbs be farther apart and closer to the glass?


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## terrydolin (Mar 31, 2008)

I found this in printwear so I answered one of the question 

Understanding undercutting 

Point light-source screens must be exposed by only one light source. That light should be as small as possible and very intense. Exposure units with more than one bulb are good for simple spot colors and text, but may not reproduce half tones, fine lines and details accurately. We’ll define “accurately” as the half tone dot or other image in the screen that must match the dimension of the image in the positive exactly.

To explain further, let’s say you have a vase on a table next to the wall. You turn the room lights out and shine a small, powerful light from across the room at the vase. The vase will cast a shadow on the wall. If the light is small and the vase is a substantial distance away, then the size of the shadow will match the size of the vase.

By contrast, now let’s say there are three lights, each several feet away from each other, shining at the vase. The light in the center creates the shadow. The lights on either side illuminate the wall behind the vase. The shadow on the wall is reduced in size or eliminated. This is an example of “under cutting,” caused by light projected at an angle toward the image (or film positive).

When an image is under cut, the emulsion under the edge of the black film positive is exposed and will not wash out of the screen. The part of the image that does wash out is smaller than the image in the film positive. Lines in the image that are supposed to butt-register might be left with a gap. Half tone dots will print smaller than called for by the color separation thereby reducing color strength or skewing color.


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