dark room design

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mshields

Senior Member
Location
Boston, MA
I have a client who would like to have what he is referring to as a 3 way switch in a dark room such that one position is for the red light, another position for the white light and a third position for off.

Obvioulsy not what we typically think of as a three way switch. Although his 3 way switch probably fits the name better.

In any event, is anyone familiar with this type of arrangment. Who makes such a switch?

Thanks,

Mike
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Most likely a single pole double throw. They stock them at my supply houses, and I do use them for darkroom lighting applications.
 

xformer

Senior Member
Location
Dallas, Tx
Occupation
Master Electrician
I have a client who would like to have what he is referring to as a 3 way switch in a dark room such that one position is for the red light, another position for the white light and a third position for off.

Obvioulsy not what we typically think of as a three way switch. Although his 3 way switch probably fits the name better.

In any event, is anyone familiar with this type of arrangment. Who makes such a switch?

Thanks,

Mike

Think what you are talking about mike, would be a 3 position switch.... not a 3-way switch.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What you're asking for is a single-pole, double-throw switch (like a 3-way), but with a center-off position. Leviton and others certainly make them, but you can do the same with a single-pole switch feeding a 3-way switch.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Mike, if yuor customer is relocating existing luninaires to a new location, a SPDT switch as mentioned above is the ticket. If this install requires the purchase of new, you can get the darkroom light, in-use light and switch as a package deal. A bit pricey though.
 

benaround

Senior Member
Location
Arizona
You want to use the dark room, you open the door and flip a single pole sw that sends

the power to the 3 way sw. at the work area, the room light comes on because thats the

way you left it the last time when you were done. To use the 'red' light, flip the 3 way and

it comes on, and so does the 'warning' light outside of the room. when you are finished

flip the 3 way and the room light comes back on all the 'red' lights go off, flip the s.p. sw

on the way out just like any other room.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100519-0709 EST

I suggest that switching between safe lights and room light is wrong. Leave the safe lights on all the time you are in the darkroom and may use the safe lights.

The problem with switching between the two types of lighting is bulb life in the safe lights. Generally these are 15 to 25 W bulbs, sometimes 7.5 W. Inherently shorter life because of the fine filament. Excessive switching on and off does not improve life.

In fact what would be wise is to run considerably reduced voltage to the safe lights. A 15 W bulb and a !A filter at 60 V is probably adequate light. If not go to a 25 W bulb.

I leave my safe lights on all the time that I might use them. I switch the white light on and off as needed.

The best method of getting a fixed reduced voltage is with a stepdown transformer because this provides a continuous sine wave, a Variac if you want adjustability. A phase shift dimmer will probably shorten lamp life compared to a comparable full sine wave. However, I have some fine filament lamps that I have run continuously on a phase shift dimmer for 35 years at a very reduced voltage, dull orange, with one bulb failure out of about 20 lamps.

.
 

Nickarus

Member
Location
Olathe, Kansas
Here's another approach that was initially presented to me for a vet clinic retrofit:

Doctor's had a 2-gang toggle switch situation for their x-ray darkroom development filtered (red) and unfiltered (white) lights. They reported repeated problems with their nurses and building maintenance crew accidentally turning/leaving on the white light while development was occurring (there was no "in-use" light).

Solution desired was to use a single toggle switch for the red light, and a keyed switch for the unfiltered light. Key was chained to a hook in the wall near these switches. I've carried this design approach over to (human) medical office development rooms without issues.

It's probably wise to simply ask the owner/end-user whenever possible to see if there's an arrangement they're already used to.
 
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