LED based Becquerel development

[Andy Stockton]

Well based on Irv’s chart in the “My latest” thread and the discussion started by Jon Lewis about a year ago it looks like a “super red” InGaAIP – Indium Gallium Aluminum Phosphide might have the desired effect.

The chart also says the output for a super-red LED is 3500mcd @20mA. For some of you with a better grounding in science than I have, is that going to be bright enough (assuming a short distance to the plate)?

The only measurement I have taken of my Becquerel development apparatus is as follows: Philips Halogena 70 Watt BR4 indoor flood lamp produces 1280 lumens giving an EV of 13.9 at 7 inches away.

Is it possible to compare those measurements?

[Andy Stockton]

I also noticed that the company that produced the chart Irv posted (OkSolar sells a 12″ diameter red traffic signal bulb for $188.50 plus shipping. Since those are produced in large quantity, that may be the cheapest way to go.

[Jon Lewis]

In doing a bit of research about this it seems like there might be problem with using lumens or candelas as a means of measuring light output for becquerel purposes. Both units of measure are weighted for the wavelength sensitivity curve of the human eye. Since the human eyes is more sensitive to greens than reds, measuring one white source and one red source will give two different numbers even if the power output is the same. I think it would be better to somehow measure the power per unit area of only the light which hits the plate (red light hopefully).

Another issue to consider is the angle of radiance of the LED.

Anyway, I was also looking into red cold cathodes <http://www.oznium.com/cathode-kit>. It might be easier to get them to cover larger areas than LEDs but I’m not sure if they’d be as efficient. Also, I think they do give off some heat but not as much as normal fluorescents or especially incandescents. Haven’t been able to find out much about their wavelength…

[phuphuphnik]

If you want to build your own board, it would be considerably less than the 12″ traffic light.

Most places that sell LEDs have specs as to light output. Try Ledshoppe, and superbrightled.com

The other thing to worry about is any pattern the die may leave. By this I mean the lens on the LED might focus the shape of the emitter. To get by this you can scuff the lens to make it diffuse. Also use more than one! This is a pretty good idea, and could lead to a very portable Beq darkroom. I have some red tail light leds left over, I’ll give it a whirl after my other experiments.

[phuphuphnik]

We use these at work, buggeringly bright! Also note the spec sheets.

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fspecs%2Fhf3-r5570.htm

Cheers!

chriso

[Andy Stockton]

There was a forum on the site that Jon Lewis posted that said the highflux LEDs get pretty hot. If you have used them at work have you noticed that issue? I thought LED’s were not supposed to do that – maybe the other components in the module?

[phuphuphnik]

LEDs can get hot, and even burn themselves out. The high watt ones are what you have to worry about. The Luxeon and the like need to be mounted on heat sinks. A sheet of copper would work, if your average Daguerreotypest can find one of those…

LEDs run cooler in general, but keep in mind a 5 watt LED still is taking 5 watts of power, what isn’t going into light is heat. My little soldering iron is only 12 watts. It won’t get as hot as the 500W halogen I use now for Beq.

The LEDs I linked to don’t get that hot.

[Pobboravsky]

At first I thought an amber (or yellow) LED would cut Becq-dev time compared with a red array. I was wrong. I assumed incorrectly that the amber LED would be emitting both red and green light. It actually emits yellow/amber light centered on ~590nm. (Similar to a low-pressure sodium light.)

It may very well be that either a green or red LED could be equally effective at Becq-Dev. Or even a yellow/amber LED. Depends upon the available effective intensities. By effective I mean the development response of the daguerreotype plate.

[Pobboravsky]

Just learned that LEDs come assembled in flexible and rigid strips.

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Flight_bars-rigid.html

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Flight_bars-flexible.html

[Andy Stockton]

Irv – is there already anything published on the wavelengths that produce the Becquerel development response? Creating an LED developer seems very do-able, it is just a matter of deciding which LED type to try first. Knowing the specific wavelengths would make that easier – if there are multiple peaks it might even be a good idea to mix more than one color into the array as long as the plate-to-array distance was such that full overlap of colors occurred.

[phuphuphnik]

That seems pretty easy, just find what colour amberlith really is. There must be a roscoe number for a similar theatre gel. I’ll poke around and see if I still have a swatch book. that’ll have it.

[Pobboravsky]

Andy: I know of no published data on the most efficient wavelengths for Becq-dev. However I am reasonably certain that a wide band of wavelengths (say, from 550-700nm) will work. I used a transparent yellow plexiglas panel and a tungsten lamp for Becq.-dev. See Figure 21, p.41 of Study of Iodized Daguerreotype Plates.

Reading the Wikipedia entry on LEDs makes me believe that using a bank of LEDs for Becq. Dev has a high probability of success. http://en.wikipedia.org/wiki/Light-emitting_diode

Some interesting tidbits:

Quote:

The development of LED technology has caused efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s. It is called Haitz’s Law.

– there are LEDs that emit both red and green light (which looks yellow). I think that would be good for Becq.

– there are computer monitors that use R,G,B LEDs instead of a fluorescent tube + filters. I think that it would possible to display a yellow screen (R+G LEDs on — Blue LED off) to see its Becq-dev possibilities.

– there are organic LEDs (OLEDs) on flat panel TV sets that are said to produce spectacular images (I’m assuming here that spectacular means high brightness)

[Pobboravsky]

RED LED panel, ~12 x12 inches, 225 LEDs $41.00 free shipping.

Product Features

* Body material: Thermoplastic

* Circuitry board material: Diecast Chrome Color: RED

* 225 RED light LEDs: 650nm (nanometer) wave length

* Working Voltage: 12V or 110V-220V

* Power: 13.8 Watts Dimensions: 12 ¼ inches (30.5cm) square

Product Details

* Shipping Weight: 2.3 pounds

I wonder if this will work for Becq-dev?

12volts – wonder if it can be powered by cigarette lighter in car?

Almost seems too good to be true.

[photolytic]

These are available on EBay for $33.99 w free shipping.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320480419983&ssPageName=STRK:MEWAX:IT

225 LED Hydroponic Plant Grow Light Panel 14w all Red

Item condition: New

Time left: 2 days 11 hours (Jan 30, 201003:45:34 PST)

Price: US $33.99

Shipping: FREE shipping

1 – 14w Xen-lux LED panel

120v 5′ power cord

Specifications:

Number of panels: 1

LEDs per panel: 225

Total LEDs: 225

Color: Red

Power per panel: 14w

Panel size: 12.25″ x 12.25″

Panel height: 1.5″

Frame: Composite

Red wavelength: 630 nm

Rec. coverage: 4 sq. ft.

Max. coverage: 65 sq. ft.

Use: Indoor growing

Shipping weight: 4 lbs.

Also available in multiples of 2@$62.99

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330393599880&ssPageName=STRK:MEWAX:IT

and multiples of 4@109.99

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320480419986&ssPageName=STRK:MEWAX:IT

[Pobboravsky]

Feasibility of Red LEDs for Becquerel Development (BD)

I was so intrigued by the possible advantages of using red LEDs for BD that I bought a PAR38 168 LED Grow Light BUDDING LOWERING FRUITING, red , (It cost $30 + $5 shipping.) It has 168 red LEDs in a circular array and runs at 120 volts, 11 watts.

This is 92mA for all 168 LEDs; 0.55mA for each LED. This is definitely not a high-intensity LED.

There are higher intensity red LEDs but they cost more and my aim was limited to seeing if it would work at all for BD. If it worked with this 11-watt array, development time would be shorter for higher wattage units. The diameter of the circular array was 12cm (4.7 inches) limiting the plate size to 3.25 x 4.25 inches.

Result: These low-intensity red LEDs did work for BD. However, a tungsten bulb + Rubylith are easier to implement and also cost less.

---

Here are some of the observations from the preliminary exposure-development test on an iodized plate. By shifting the dark slide, subsequent thirds of the plate were given 5, 10, 15 minutes exposures. These exposures correspond to 20, 40 and 60 times what is needed to expose an I-Br-mercury-developed plate.

• After 3 minutes BD a faint image was visible when viewed at an oblique angle. However, no image was seen when the plate was viewed at 90 degrees, just a very hazy opaque appearance.

• Development was stopped after two hours. The developed image looked strong and brownish in hue.

• After hypoing for 2 minutes, rinsing and drying the image weakened considerably and the hue shifted to blue. The plate was not gilded.

• There was zero fog in the shadows; the LEDs were just slightly warmer than room temperature.

• The 15 minute camera exposure gave the strongest image. This corresponds to 60 times what would be needed for an I-Br-Hg plate. This is an ISO speed of 0.00083; this agrees with the ISO speed published in Study of Iodized Daguerreotype Plates.

• The illumination intensity of the circular LED-array seems to be greater in the center of the field, but that is uncertain. A square array of say 10-inches on a side would yield a more even intensity while covering larger plates.

I wonder if image weakening in the hypo stage can be minimized by boiling the water used to prepare the hypo solution. Boiling drives off dissolved gases. After allowing it to cool to room temperature add 15g sodium sulfite. After that is dissolved add 15g sodium thiosulfate to make a liter of solution. Decrease hypoing time to a minute.

The major advantages of BD with high-intensity LEDs are: 1. Much shorter development times, and 2. little or no fog depending upon how warm high-intensity LEDs turn out to be.

[Pobboravsky]

The 20 mA of the high-intensity red LED in phuphuphnik’s link is 36 times the power of the 0.55 mA of the LED I used in my cheapo test. I would imagine that a square array of the 20mA LEDs would reduce Becq-Dev’ment time by a lot.

(Phuphuphnik: love that that name; it is so-o-o melodious)

A hearty dark bread could be called Phuphuphnikel. I’d best take 2 aspirins and lie down and hope I’m better in the morning.

[Andy Stockton]

What was the distance between the array and the surface of the plate? When I have examined different LEDs the lens design had a big effect on the shape and intensity of the light beam. I was worried that I might get a disconnected pattern of circles of strong development surrounded by weaker areas. Did you increase the distance to avoid “spots”?

What interests me about this approach especially (besides no fan and lower power consumption) is the idea of creating a developer that could run on my car battery. I someday aspire to take images somewhere besides my back yard, and being able to start a controlled development cycle while the latent image is still fresh seems a good thing.

[photolytic]

Andy, Not a problem.

Low cost 400watt power inverters that plug into a car’s 12 volt outlet are available for <$50.

Higher watt inverters are available but they may blow the 20amp fuse unless you clip them to the battery terminals

I bought the 225 array of red LEDs in a 12×12 fixture but have yet to try it out.

I’d be interested in how close it needs to be to the BD plate.

Incident light readings at distances from 2 to 12 inches from the array are 6.2-7.4.

[Pobboravsky]

Andy,

My test was done with the LEDs 10-inches from the plate. The EV was 6.7 as measured with an incident meter (ISO set at 100). Very similar to Photolytic’s readings.

Is there a hotspot for each LED on the illuminated surface? It is of course a concern but the only question I was asking of the test was: Would it even work for BD? As you pointed out illumination uniformity across the plate surface could be affected by the design of the LED.

Phuphuphnik said:

Quote:

The other thing to worry about is any pattern the die may leave. By this I mean the lens on the LED might focus the shape of the emitter. To get by this you can scuff the lens to make it diffuse.

.

The light can be diffused in a number of ways (opal glass,for one.)

[phuphuphnik]

Pobboravsky: I love your rye humour. Anyone try cold cathode lights? I’ll ‘borrow’ a superbright array from work and take a look.

chriso

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