Light from a window AC in a darkroom

[David Brown]

My current darkroom has a standard issue window AC unit. It leaks light. I'm mitigating the problem, but I know others have similar units in darkrooms. However, I've never seen a discussion about how much light they let in (or don't). Anybody esle have a problem with this?

 

[glbeas]

I've had window ACs in the darkroom. The most frequent culprit is the fresh air exchange valve. If it's open or seals poorly you will get light. Mostly I had to do a lot of creative sealing around the sides to get the light out.

 

[Mike Wilde]

I have built light baffles for exhaust fans out of black foam core board and gaffers tape. I am sure a similar option could be fashioned here.

 

[RPippin]

I have a window unit like you describe as well and it leaks light like crazy. Not much of an issue in the winter when it gets dark around 6 o'clock, but in the summer when it's still light outside after 8 P.M. it's more of an issue. It's surprising how much light leaks in my darkroom, it's an old motorcycle shop I converted about four years ago. I've done a paper fog test during the winter months when the AC unit is covered, and although there are lots of leaks other places, I've experienced no fog. During the summer, I hang a sheet of dense black cloth from the rafters to separate where my printing station is and this helps. I also use a Thomas safelight and think this helps, although I have no scientific basis to back my claim up. I used to worry a lot more about light leaks than I do now.

 

[hpulley]

Me too, I'm not so worried. You don't need a completely dark room even for RA-4 printing. As long as the light isn't actually striking the paper you're fine so if you can even block the area under the enlarger and by the developer tray you should be fine. People go crazy for cracks and things when really there is no need for a process that takes only a few minutes until it is done fixing.

 

[jp498]

A light baffle would be a black box or tube that's open on the side connecting to the AC unit, and open on the bottom or top to exhaust air, like a snorkel or straw. I've done this to quiet the noise from exhaust fans in networking equipment.

 

[photoncatcher]

Wow! AC in a dark room? That's a luxury I can only dream of. My little basement DR only has 2 windows, and they have wooden panels to block light when I'm working. Yeah a little jealous.

 

[Mike Wilde]

No ventilation at all? I'll brag a bit here then. I have a heat recovery ventilator to vent the darkroom.
I added it to the central HVAC system in the house after I replaced the old windows, added a new chimney top damper to the woodburning fireplace and sealed every crack no matter how small.
Now with the hrv running the new windows don't stay fogged half the day after someone has a shower in the winter.

I set it up so that the intake (that get exhausted outside after going though the heat exchanger) is positioned at the end of my sink, beside where the fixer tray usually sits.

Seriously, set up at least an external exhaust fan if no other ventilation.

 

[David Brown]

Wow! AC in a dark room? That's a luxury I can only dream of.

Well, when it hits 100 degrees (F) here in Texas, it is hardly a luxury!

My prior darkroom was a partitioned off room inside the house, so I added a duct from the Central HVAC unit. Very nice. Even so, I had to put a black diverter baffle on both the incoming register and the outgoing vent to block extraneous light. On this window AC, I attached the filter material over the louvers on the outside of the case (outside the darkroom) and that knocked down most of the light. The remainder is inconsequental for printing, and I can drape a towel or something over it for the few minutes it takes me to load film.

I thought I had a bigger light problem at first, until I discovered that the majority of the light I was seeing (NOT inconsequental) was coming from the LEDs on the control panel of the machine! OK, those were covered easily enough.

 

[waynecrider]

Well as a A/C man let me tell you that the best way to stop light leaks is to build a supply and return plenum out of insulation board from Home Depot or Lowe's with silver or duct tape. Make sure you spray paint it black inside before you assemble it totally and you can put angled dividers inside for one way or two way blow. Shoot the supply out both sides or up and bring the return air in from an opening on the bottom. You can adapt the boxes to a surface with a curve, since many a/c unit covers are not flat, by using a divider to trace the surface angle to the box and then cut with a steak knife. Tape with duct tape. You may have to use some soft spray insulation as well, especially around the control box side (don't cover it) when the cover is off. The other area that leaks alot of light is the side the drain is on. Since the a/c covers usually don't fit that tight you might need a little elsewhere. When the cover is off you'll see various areas.