Halogen bulbs

[luxikon]

Since yesterday I notice an enormous increase in exposure time. Preparing new developer didn't help. Is it possible that the halogen bulb is getting weaker? The last one had a sudden exit.

Klaus

 

[bdial]

Yes, it's possible, though usually bulbs don't diminish suddenly, other causes might be a failing socket, or other connection, or the power supply if the bulb doesn't use line voltage.

 

[pentaxuser]

Most enlarger halogen bulbs have two prongs at the back of the bulb which are connected to a ceramic connector from which the wires run for power. Check that the prongs are clean. I'd clean them every month with emery paper. More importantly I'd clean inside the ceramic holder. A small round jeweller's file is ideal but a large sewing needle with wire wool wrapped around the needle should be OK. You should probably change the ceramic holder every time you have to change the bulb.

pentaxuser

 

[tkamiya]

I agree with Pentaxuser. Halogen bulbs gets so hot that, over time, clips in holder that makes electrical contact to the bulb's terminal no longer makes good contact. In addition to cleaning the clip and the terminal, you may have to GENTLY bend the clip toward the bulb so that pressure applied to the contacts are strong.

I had to do this to many of household halogen lamp fixtures after few years.

 

[RalphLambrecht]

Since yesterday I notice an enormous increase in exposure time. Preparing new developer didn't help. Is it possible that the halogen bulb is getting weaker? The last one had a sudden exit.

Klaus

When you need more exposure, you prepare new developer? I didn't get that one.

Yes, halogen bulbs get weaker over time. Their light also gets 'warmer' (more red, lower K). The same happens to incandescent bulbs, fluorescent tubes, CFLs and the sun. Luckily, it takes a long time for the last to show the effect. About the only light sources, not affected by time during its lifetime, is a candle and a lightning bug.

 

[luxikon]

I thought the developer might be exhausted. Why is this idea so strange?

Klaus

 

[ricksplace]

www.replacementlightbulbs.com
I bought some replacement enlarger bulbs from these guys. Good place to deal with. Cheap prices too.

 

[fschifano]

Yes, halogen lamps do become more dim and more red over time, and this will increase your exposure time. Compared to the more standard types of incandescent lamps though, halogen lamps tend to be pretty stable for most of their lives, then die suddenly as you've noticed. Perhaps this lamp is an exception to the rule. In any case, the lamp is very likely nearing the end of its lifespan and should be replaced. Examine the socket for traces of corrosion or oxidation. Clean or replace as necessary. That should fix it. You might also want to check the inside of your light mixing box if the enlarger is so equipped. The inside of the mixing chamber for my Chromega II lamp house had yellowed over time from the heat and intense light of the halogen lamp. I re-lined it with new white styrofoam and the difference was dramatic. Printing speeds were cut in half and contrast went up I estimate about a grade with papers I'm using. I had to recalibrate everything, but now I know. When the foam liner in the mixing box starts to get old, I change it out.

 

[RalphLambrecht]

I thought the developer might be exhausted. Why is this idea so strange?

Klaus

The first sign of exhausted developer is an inability to develop Dmax. More exposure won't fix that, but extending the development time will fix it within reason.