DIY LED Exposure Unit

[blue moon]

Other way around. I'm aiming for a 7 and I'm doing better than that because I'm at a 9 (which is slightly over exposed).

I must be missing something. On a Stouffer scale, 7 is exposed longer than 9. If you don't do anything, all the numbers will wash out (that would be 21). With a 10 second exposure, you should get something like a 12 (based on your numbers). Going to 50 seconds, would reduce the number and leave the 7 intact.

Can you post a picture of the strip and what it looks like on the screen after exposure?

pierre

[Pangea]

Absolutely, check out the photos below. I lost the sleeve for the strip so I may be totally wrong and misunderstanding the guide from the website:

http://www.stouffer.net/using21step.htm





I should probably get a new strip soon too 

[blue moon]

DUH!!! You are right! I was thinking backwards. Glad I asked for a photo, it cleared it instantly. The picture is worth a thousand words!

pierre

[Pangea]

DUH!!! You are right! I was thinking backwards. Glad I asked for a photo, it cleared it instantly. The picture is worth a thousand words!

pierre

Whew, I thought I was going nuts haha. Thanks for double checking my work!

[Jhtitan]

At the risk of resurrecting a dead post I did have a question for you on this.

Do you have safe yellow LED's running in between the groups of UV LED's? It kind of looked like you had something running down those gaps in one of the pictures.

I am working on my own design and am considering using yellow LED's around the perimeter of the light chamber. 

Thanks
Jon

[Pangea]

I do but I never hooked them up as I don't really have a use for them. I have a little jig I built to line up positives on the screen, it's not fancy but it only cost $30.

[Fiodor Petrenko]

I'm in the process of rebuilding my LED exposure unit and figured I would document it here.

Through looking at some tech sheets it looked like most emulsion crosslinks at about 395 nm wavelength. I was surprised to find this wavelength was available in inexpensive strips and 2 density layouts. I opted to get the densest at 120/meter rather than 60/meter because more = better, right?

I ended up using 11 34" strips mounted on a piece of coroplast that was then stapled to a box made of 1"x4"s. It looks pretty janky and like a fire hazard which is the reason it's getting rebuilt.


The power supply is 120v AC in and has two 12v DC outputs that are rated at 10 amps. The time controller was purchased on eBay and pretty much interrupts the 12V DC circuit when the time is up, shutting off the LEDs. The switches on the laser cut control panel turn all the power on, start the timer and turn on safe lights (yellow LEDs). I intended to purchase glass at some point but it was never needed because I use a space saver vacuum bag for exposure. For the new build I'll probably end up adding glass and a proper vacuum lid in phase 2.

I plan on reusing the time controller/switches and the power supply but not the LED panel or box. This time around I ordered 4200 LEDs because I want the strips to be much closer together like the M&R Starlight/Workhorse Lumitron. The strips will be soldered this time instead of using the crappy snap connectors and will be done in parallel to avoid differences in brightness. If they're wired in series the end strip has voltage drop and the whole exposure would be uneven.

So now for the before pictures:

Wiring Diagram


Turned on


Janky Wiring


Control Panel Mock Up


Control Panel Finished


First Tests (WBP Emulsion)


Switched to Cryocoat with 18 second exposure




Final exposure time using a Stouffer 21 step is ~80 seconds. I'm curious (and I'm sure someone here can answer) when companies are advertising their exposure units can expose in 10 seconds, are they using the 21 step guide?


Anyway, I'll update this thread when I start the rebuild and make sure to add any updated documentation (wiring diagram). Until then, ask any questions if you have them!


UPDATE:

Redrew the schematic during my morning coffee

Hi! I'm wondering if you used 5050 uv leds. I will try these and I'd like to know if they'll work fine:

Specification

    Input volts: DC 12V (12V 2-3 A for 5meters 3528 300LED light strip)
    Wavelength:395-405nm
    Long life span 50,000+ hours
    Protection Rank: iP 65waterproof
    PCB Color: White
    Is Dimmable: Yes(dimmer required)
    Is Trimmable: Yes(cuttable every three LEDs)
    Drive Mode:Contant Voltage
    Beam Angle:120°
    Viewing Angle: adjustable by mounting position
    Working Tempreture:-20° to 50°
    Size: W1.0cm x T0.25c


Did you tried the exposure unit on diazo?

Thanks!

[Pangea]

I used 3528s that are spaced about 3 per inch, the densest I could find. WBP is a diazo emulsion and it worked just fine with longer exposure times (45 seconds-1 minute if I remember correctly). I've since switched to photopolymer and expose at 20-25 seconds but may switch back again to compare details.

[Doug S]

Fiodor,

Thanks for posting the pics.  I think you'll be much happier with the leds closer together.  The pic you posted of the lights spaced out like that looks a lot like the lawson unit I bought "I've since went back to metal halide".  The lawson was fine for the majority of the work I do but I wasn't happy with the halftone exposures.   I know the starlight has roughly 10 times the leds which eliminates the cold spots. 

Another thought:  I admire you guys that have the knowledge to even attempt building your own because I wouldn't know where to begin.

[Fiodor Petrenko]

Hey, Doug, how are you? The work is from Pangea, not mine, so props to him. I will be starting mine next week.

The widht of the strip i'll be working with is about 1 cm, so I'll put one strip (1 cm. empty space) another strip, etc. until i cover 1 mt. lenght.
As I measured, the space between every led light is about 0.65 mm. and the distance between the glass and the lights will be about an inch. What do you think?

[blue moon]

Hey, Doug, how are you? The work is from Pangea, not mine, so props to him. I will be starting mine next week.

The widht of the strip i'll be working with is about 1 cm, so I'll put one strip (1 cm. empty space) another strip, etc. until i cover 1 mt. lenght.
As I measured, the space between every led light is about 0.65 mm. and the distance between the glass and the lights will be about an inch. What do you think?

if the distance between LEDs is 0.65, the distance between the strips should be the same.
the distance to the glass will depend on the angles of the light the LEDs are producing.
You will also have problems with heat if you are only 1" away. Heat will kill your light source and it will also degrade the light output much faster.This in turn means you will have to adjust your exposure times often.

pierre

[Fiodor Petrenko]

Hi, Pierre, I was considering what you said before on the thread. When you say " angles of the light the LEDs are producing"
you refer to the beam angle of light? the manufacturer specifies "120º beam angle", I don't know if this is useful information.

Is there an accurate formula to calculate the distance between the lights and the glass?

Thanks a lot for the advice, is very helpful for the beginners!


 

[blue moon]

Hi, Pierre, I was considering what you said before on the thread. When you say " angles of the light the LEDs are producing"
you refer to the beam angle of light? the manufacturer specifies "120º beam angle", I don't know if this is useful information.

Is there an accurate formula to calculate the distance between the lights and the glass?

Thanks a lot for the advice, is very helpful for the beginners!

yes, the beam angle. 120 seems to be the most popular. . .

yes, there is a way to calculate the spacing, unfortunately I don't have that formula. Easy way would be to get a UV meter and measure the field than keep tweaking until you get uniform readings.

pierre

[mk162]

I know it would increase the exposure times, but wouldn't a diffuser help with the hot and cold spots?

It'll be a tough sell to get me away from my 7500k Amergraph.  I do screens in about 15 seconds...2 up.

[Sbrem]

I know it would increase the exposure times, but wouldn't a diffuser help with the hot and cold spots?

It'll be a tough sell to get me away from my 7500k Amergraph.  I do screens in about 15 seconds...2 up.

You might consider the power draw with the Amergraph. We just got the Saati ProLite 450, to replace a Violux 5000S (5K) and so far exposure times are similar to the Violux, but we still have considerable testing to do. Currently, we use Saati HU42 and Ulano Orange, and we're about to text Murakami T9... The ProLite is closer to a point source than a bed of LED's, but not as small as a MH bulb.

Steve