UV bulbs burning out?

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pfrand

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I have a home made UV exposure box that uses six F15T8-BL bulbs. One of the bulbs is starting to go (doesn't light up fully). I am wondering if I should just replace the single bulb, or if all the other bulbs are most likely also going to start burning out soon, in which case
I would replace them all. The bulbs are at least five years old. Does anyone know anything about bulb life?

Thanks,

Peter
 

Nicholas Lindan

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UV lamps are fluorescent lamps without the fluorescent coating, if that is tautologically possible. Try reversing the flickering lamp - don't know why that works but it did with my shop lights.

Fluorescent lamps don't normally go bad with the passage of time. It takes on-hours for them to wear out. If you have had one go bad this early it is probably due to a manufacturing defect. You should only have to replace the one lamp.
 

fgorga

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In my experience, when one bulb goes weird others are likely to as well. The bulbs do have a finite lifespan and recommend replacement cycles are most likely listed in the specs for your bulbs. However, it is unlikely you have reached this limit since alt process use is lots of on and off for short times rather than continuous use. Have you tried reseating the balkly bulb? If the electrical connection is bad that can cause problems.

Rather than replacing the bulbs, I would consider replacing the bulbs with LED strips, I did this a while back and have been very pleased. Take a look at this thread for more information on this... https://www.photrio.com/forum/threads/diy-uv-box.180065/#post-2354103
 
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pfrand

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Thanks a lot for all the responses. I had no idea you could use LED bulbs for UV light. Sounds like they are about twice as strong as the fluorescent bulbs I have been using. Standard cyanotype exposure with my lights is about 18 minutes. Any recommendations about good places to buy them? Amazon I guess?
 

fgorga

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I used these strips (link to Amazon) to retrofit my homemade unit that originally had fluorescent bulbs.

Initially, I installed four strips. Then several months later I added another four strips.

My unit will hold a 16x20 inch print frame. Print times are about 7 minutes for a salt print. I don't do much cyanotype and so I don't think I have any data on exposure times since installing the second set of LEDs.
 
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BrianShaw

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Initially, I installed four strips. Then several months later I added another four strips.
How far apart are the strips and how even is your coverage? This looks like a very economical way to build a UV printer!
 

fgorga

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How far apart are the strips and how even is your coverage? This looks like a very economical way to build a UV printer!

Brian,

Now that I have 8 strips, they are on 2 inch centers. I added the second set between the original strips which were thus on 4 inch centers.

The inside of top of my box sits 8 inches off the table. Give roughly an inch for the LED strips and an inch for the print frame. Thus the glass of the print frame is roughly 6 inches from the glass of the print frame.

The box is painted a glossy white.

Here is a photo of the inside of my box:

IMG_20221214_165727417.jpg


The blue electrical box is left over from when I had fluorscent bulbs installed and is not necessary with LEDs. Also, I don't think that the circular vent holes I have are needed with the LEDs as they run much cooler than the fluorescent bulbs. However, I have not tested this.

The light is very even. I do not trouble with uneven exposure. I generally print in an 8x10 frame; often two under the UV at the same time. The largest I have printed is an 11x14 image in a 16x20 frame.

Take a look at the alt process galleries on my website (https://porfolio.gorga.org/). The large majority of these prints were made with my homemade box.

I have been very happy with my retrofit. I was having trouble with balky fluorescent bulbs (remember the original post in this thread!) that were at least a decade old when I decided to retrofit with LEDs rather than replace the bulbs. I have zero regrets with this decision.

Regards,

--- Frank
 

koraks

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@fgorga aren't you tempted to stick more strips in the big spaces between the current ones? You should be able to reduce exposure by more than a stop this way, at marginal cost and with no performance penalty otherwise.
 

fgorga

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@fgorga aren't you tempted to stick more strips in the big spaces between the current ones? You should be able to reduce exposure by more than a stop this way, at marginal cost and with no performance penalty otherwise.

@koraks, generally I have not really been tempted to add more strips. For most processes I do exposure times are less than 10 minutes which is plenty fast enough for the way I work... I am old and slow! 😉

However, this summer and fall I've been experimenting with cuprotype with exposures of 45 min, so the thought of adding more strips has crossed my mind more recently. I've just not acted on that thought and I'm not sure I will. My preffered processes are salt printing and Pt/Pd and I'm pretty sure cuprotype will be an occasional process for me, just as is cyanotype.

If I do add more strips, you folks at photrio.com will be the first to know!😀
 

koraks

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Well, I'm known to be dangerously impatient, so 10 minute exposures are virtually unacceptable for me :wink: Alt. processes can really be all over the place when it comes to exposures, but it's really nice IMO if they remain limited to just a few minutes.
 
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