Safelight bulbs?? - rec.photo.darkroom

Message from discussion Safelight bulbs??

Jean-David Beyer

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More options May 4, 9:24 pm

Newsgroups: rec.photo.darkroom

From: Jean-David Beyer <jeandav...@verizon.net>

Date: Mon, 04 May 2009 11:24:38 GMT

Local: Mon, May 4 2009 9:24 pm

Subject: Re: Safelight bulbs??

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Geoffrey S. Mendelson wrote:
> I have a Kodak safe light that looks like a metal cone. One end screws into
> a lamp socket, the other holds a round filter. It's probably from the 1960's
> or older, but it's the only thing I could get here in any color except red.

> I bought out the last of the locally availaible little red things that
> use nightlight bulbs and a bunch of the bulbs, so I am covered for red,
> but I wanted an orange (Wratten OC) filter as I can see much better by
> it.

> The problem I have, is that here in Israel, we have been ahead of
> everyone else in energy saving, CFL bulbs have been sold here, and used
> by me, since 1997. That's good, but it has caused the demand and
> therefore the supply of low wattage incadescent bulbs to dry up.

> I found a few Chinese made 7-10 watt bulbs, but they only last a few
> hours. I found a 15 watt bulb sold for refrigerators, but it has a
> different base and I am trying to adapt it, but may not be able to get
> those bulbs much longer and they are very expensive being made to
> operate at 0F and below.

> The smallest incadescent bulbs that are still common here are 40 watt
> bulbs.

> What is everyone else doing for safelights?

I use 7 1/2 watt 120 volt incandescent lamp bulbs. Whereas most incandescent
lamps are designed to last about 750 hours, these little ones are designed
to last 1250 hours. I do not know if I have ever had one burn out. Now if
you run them at 220 volts, their lifetime would be very short.

My safelights came with 15 watt bulbs, and they did not seem to fog paper,
but since the lights are slightly less than the 4 feet distance from my
working surfaces, I thought it would be better to use smaller lamps in them.

Incandescent lamps run much longer as their input voltage is reduced. You
might consider putting a suitable resistor in series with the bulb to dim
the bulb slightly and increase its lifetime. The trick is to compute the
proper resistance. If you measure the resistance of the bulb with an
ohmmeter, it will be very low, so you will get too low a value to put in
series. It is better to calculate it. If it is a 22 watt bulb at 220 volts,
the bulb draws 1/10 amp, so it is 2200 ohm with a hot filament. So you might
try a 110 to 220 ohm resistor to lower the voltage. You might wish to use a
5 watt resistor.

> Thanks in advance,

> Geoff.

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