Cfah2002a-rmi-jt & cfah2002y-rdi-et

[Urahara]

Hi

I am looking for LCD modules to be used in a B&W film photography darkroom environment where the material used is sensitive to all colors of light except red.

I found the above two that I think are suitable for my project, since both have red LED backlight and can be used in the dark. I have some questions :

1) The less expensive version, CFAH2002A-RMI-JT uses STN negative but I notice the mention of "blue" in the technical specs. Does that mean that there would be blue light when it is being used? Do you happen to know what is the wavelength of the red (and blue?) light emitted?

2) CFAH2002Y-RDI-ET uses FFSTN and "near black". Any other colors involved that is not black ? Also, what are their wavelengths?

Any other relevant info would be appreciated too.

Thks!

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[Heffo]

Having done quite a bit of B&W darkroom work myself in my high school days, my suggestion would be to get a white backlit module and put a darkroom light filter over the display.

That way you don't have to worry about possibly ruining photo paper stock with a display with a slightly off wavelength.

 

[CF Tech]

The filter is in interesting idea.

As far as the red backlit modules, the only color light would be the red. The "STN Blue" and "FFSTN Near Black" refer to the characteristics of the LCD in front of the backlight. But they can only filter the light produced, they do not make any light on their own.

 

[Urahara]

Thks!

I did consider putting a red filter in front of a white-lighted LCD. This would involve getting a filter (such as a pdt called Rubylith) which I have no easy access to over where I live. Also, having a filter creates another "point of failure" since white light might leak from the filter (weak glue bonding due to aging). Finally, having a filter in front of the LCD weakens the final light output, although i must say i hv not tested if it is still acceptable though.

Since only red light is ever emitted, think it should be good.

 

[Urahara]

The filter is in interesting idea.

As far as the red backlit modules, the only color light would be the red. The "STN Blue" and "FFSTN Near Black" refer to the characteristics of the LCD in front of the backlight. But they can only filter the light produced, they do not make any light on their own.

Hi CF Tech

Something just occurred to me as odd, so I thought I ask. If the STN Blue or the FFSTN Near Black filters the red led, wouldn't there be any color emitted?

 

[CF Tech]

You might think of the LCD as a "switchable filter". When the LCD is blocking, the LCD has one filter characteristic, and when it is clear it has another.

 

[Heffo]

I done a bit of cross-referencing between the sensitivity curves of a few different brands of B&W Photographic Paper (Agfa, Kodak, Ilford) and the wavelength of light emitted from red LEDs.

Of all the red LEDs I found, the emitted light intensity curve dropped to zero at 600nm.
The photo paper's sensitivity curves fell away sharply after about 500nm and were pretty much completely insensitive after about 550nm, except the Ilford papers which were still sensitive but would have dropped off completely at about 575nm at my extrapolation since their graphs stopped at 550nm.

Based on that, my suggestion would be to get yourself a couple of cheap red (waterclear type) LEDs from your local hobby shop, do some exposure tests on your paper stock and develop the papers to see if you get any exposure from the LED's and if that works out, then splash out and buy the RED LED model LCD you are after and try some more testing with the unit.

Makes me want to get back into darkroom work now!