# PCB exposure box - bulb burnt. Options for replacements

#### mik3ca

##### Member
I have purchased the following UV exposure unit about a year ago to make my PCB's:

It had done a good job but now I have a "wear-and-tear" problem.

As of last light test (I put the lights on for 1/2 a second), the 2nd bulb from the back is completely off, and the rest are completely on except for the one closest to the front which is pinkish in color. Also the ends of the bulbs where light is supposed to emit is also a dark color.

This suggests to me that I need to replace the bulbs.

The problem is the local hardware stores only carry 12-inch bulbs of the same style for counter-top fixtures but I don't think they are the same. They identify them as flourescent but I read that UV and flourescent are different and its the UV that the pre-sensitized layer of the PCB needs I think.

I also checked a local electronic store online for the bulb and they don't carry it.

So far, the only solution I come up with is to bus 65+km to scarborough (to the same store where I got the exposure box from) but its ridiculous to travel that far just for a lights.

I think I did see someone once make a UV exposure unit with UV leds but how would I embed that into this box without blowing anything up? or is that even doable?

I mean I'm just trying to look for a good option so I won't have to travel 65km every time I need to replace lights.

#### dknguyen

##### Well-Known Member
Aren't UV bulbs black in colour and illuminate purple? If your old bulbs just put out white light then just get 6500K full-spectrum bulbs (do those put out enough UV? I thought you needed something like an actual black light for curing resist but maybe I'm wrong.) How long do you have to leave the board in the exposure unit anyways? Hours?

Sucks that you can't drive. I use to drive 70km to work every morning. And then back again. Maybe you should just make the trip if you're not sure. You talk as if you're replacing bulbs every week. It'd be like, what? Once a year?

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#### mik3ca

##### Member
Aren't UV bulbs black in colour and illuminate purple?
I thought they were also in white too but I could be wrong. The manual page that came with my box claimed the lights that were included were UV.

If your old bulbs just put out white light then just get 6500K full-spectrum bulbs
I dont understand the "K". is that the light intensity?

How long do you have to leave the board in the exposure unit anyways? Hours?
5 minutes a board but I'm doing alot of boards.

#### dknguyen

##### Well-Known Member
I thought they were also in white too but I could be wrong. The manual page that came with my box claimed the lights that were included were UV.

I dont understand the "K". is that the light intensity?

5 minutes a board but I'm doing alot of boards.
K is the colour temperature. As in Kelvin. You know, the spectrum of light emitted by a blackbody of that same temperature.

Hmmmm. It looks like black lights and UV bulbs are actually two different things. A black light is a UV bulb where the visible wavelengths are purposefully filtered out. A UV light is just everything including the UV and visible byproducts. I never knew. You might have to make the trip. 5 minutes sounds too short for the intensity that I would expect from a 6500K bulb.

Maybe look for places that sell water sterilization products.

#### Inquisitive

##### Super Moderator
Contact the place in which you bought the unit. Ask if they can get replacement bulbs. Have the correct part# from your present units bulbs in hand (should be stamped on the bulb). Ask for them to mail or ship you replacements via United Parcel Service. You don't have to travel. You can shop the world from a keyboard or phone (local or 800 number).

Or contact an industrial bulb supply house and have them shipped to you. There are more options if you research possibilities.

#### mik3ca

They do sell replacement bulbs for double the price of a regular flourescent bulb and shipping prices here are overkill for a bulb. Shipping rates are often $10+. Could I get away with UV leds? if so, then I might as well do just that and never replace a bulb ever #### dknguyen ##### Well-Known Member Most Helpful Member They do sell replacement bulbs for double the price of a regular flourescent bulb and shipping prices here are overkill for a bulb. Shipping rates are often$10+. Could I get away with UV leds? if so, then I might as well do just that and never replace a bulb ever
I don't think UV LEDs will play along with how penny pinching you seem to be in your previous projects. Go to youtube. Other people have built UV LED Exposure boxes. If I bothered, I would only use the box as a case and pretty much toss out all the electronics.

#### KeepItSimpleStupid

##### Well-Known Member
You want the 254 nm lamps which should be a germicidal lamp as well. You have both long and short wave UV lights.

This https://www.bulbs.com/product/TUV8T5-G8T5 is probably what you need.

Reminder - don't touch the lamps with your fingers. Some lamps you can't touch. These your probably better off not touching.

#### mik3ca

##### Member
oh ok so germicidal it is then

#### Pommie

##### Well-Known Member
Note that germicidal UV lamps are damaging to the skin and eyes. The box above looks like it is not interlocked to prevent opening with the lamps on. Unless the above box has these safety features I would not be fitting germicidal lamps. Have a read of this for more information.

Mike.

#### mik3ca

##### Member
They're damaging even when they are turned off?

#### unclejed613

##### Well-Known Member
there should be printed information on the bulb near one of the ends, a part number or type number that you can look up. i'm guessing they are standard fluorescents that have enough UV leakage through the phosphors to activate the photoresist.

#### Inquisitive

##### Super Moderator
13 entries in the thread and we still have an elusive part number.... do they just want to lament or do they want help? Sheesh!

#### unclejed613

##### Well-Known Member
yeah, 6 bulbs in the thing, should at least yield one readable part number.

#### jbeng

##### Member
The lamp I have always used for exposing PCBs is a F15T8/BL bulb. 18" length, 15 Watt, blacklight with white glass tube.
I use two at 4" distance from the contact frame & I don't use them often enough any more to wear them out.
I also can't tell if yours are 18" in length.
Here's a place that has them: https://www.bulbs.com/product/F15T8-BL

#### mik3ca

##### Member
Ok so I did try the philips 3000K light (12-inch) that I picked up at home hardware (also for sale at Home Depot) and now in my exposure box I have the new light at the back, a space, and the front has four original lights.

I tried a tiny circuit (about 1 inch square size) by putting it at the back of the exposure unit so the new light shines on it the most and the board came out pretty good. I used a 5.5 minute exposure time even though the board manufacturer recommended a 3 to 4 minute time.

I'm starting to think there is some math involved in the exposure times based on light because I heard people can use sunlight as an exposure source and I even used blacklights as an exposure source in the past before I bought my exposure unit.

#### dknguyen

##### Well-Known Member
Ok so I did try the philips 3000K light (12-inch) that I picked up at home hardware (also for sale at Home Depot) and now in my exposure box I have the new light at the back, a space, and the front has four original lights.

I tried a tiny circuit (about 1 inch square size) by putting it at the back of the exposure unit so the new light shines on it the most and the board came out pretty good. I used a 5.5 minute exposure time even though the board manufacturer recommended a 3 to 4 minute time.

I'm starting to think there is some math involved in the exposure times based on light because I heard people can use sunlight as an exposure source and I even used blacklights as an exposure source in the past before I bought my exposure unit.
You worded things as if you still have other UV bulbs in there right? You can't gauge the effectiveness of the regular fluorescents aren't the only ones in the box. I'd expect a dying UV bulb to put out more UV than a regular fluorescent bulb, let alone a 3000K one. Because if they are putting out enough UV to expose a PCB, then I better change out a bunch of the bulbs in my house and workstation.

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#### mik3ca

##### Member
The other "UV" bulbs are at least 3 inches away. The noticeable difference between the bulb types when turned on are the colour. the "UV" ones are light purple and not-so-bright and the new one is more white yet brighter.

#### dknguyen

##### Well-Known Member
The other "UV" bulbs are at least 3 inches away. The noticeable difference between the bulb types when turned on are the colour. the "UV" ones are light purple and not-so-bright and the new one is more white yet brighter.
In other words that wasn't a reliable test. You still have no idea how effective the regular bulb is because you have no control group for your experiment. The other UV bulbs are still in there exposing the PCB and you have no idea how much a PCB placed in that location with no active bulb above it.

Normally, you would test this by only have regular bulbs so that your control group is just "not exposed". Do that, or remove remove the regular bulb and expose another PCB in the same location with no bulb above it and see how well it exposes.

Did you learn the scientific method in school? The test as you did is like replacing the leg on a 4 legged table with a piece of celery and saying "The table hasn't fallen over, which means that the celery must be effective at supporting the table", forgetting that the other 3 legs can still hold up the table, just not as well.

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