LED bulb

baachitraka

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Ron789

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I'm not familiar with this bulb but looking at the shape (not round) and material (not opal) I would certainly not recommend it. And beware: 150W halogen will produce lots of heat.
 

Ron789

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Hello Ron,
I would be interested in more information regarding the led bulb you mention for your 138s. Can you elaborate on the specs - wattage, approx size, etc. any chance seeing a photo of it mounted in the 138s.
Regards RD

I did some research and learned that this bulb is a:
Aigostar E27 LED Globe 20W=170W White 6400K 180° 230VAC
The diameter is 12 cm.

IMG_20171103_004558137

Aigostar E27 LED Globe 20W=170W Wit 6400K 180° 230VAC
mounted in a Durst L138s

IMG_20171103_004500735

Aigostar E27 LED Globe 20W=170W Wit 6400K 180° 230VAC
mounted in a Durst L138s
 
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emeraldcity_grain

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I did some research and learned that this bulb is a:
Aigostar E27 LED Globe 20W=170W White 6400K 180° 230VAC
The diameter is 12 cm.

I really appreciate this information Ron.
I am assuming your 138s LED setup provides ample coverage for 4x5, which is the format I use this particular enlarger.
Looks like it's time for me to look at my equivalent options available to me here. Though in a 120v E26 base.
Thanks again.
 

Ron789

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emeraldcity_grain said:
I am assuming your 138s LED setup provides ample coverage for 4x5
Click to expand...

Yes, I use it for 4x5.
But frankly, you don't really need such a large bulb to get acceptable even coverage. I tested the coverage with a 150mm Rodagon lens stopped down to F/16. I used a Gossen Sixtolab to measure the brightness across the entire image, without a negative in the carrier. I double checked the Sixtolab results using a Sekonic light meter.
With a regular size bulb of 7,5 Watt the Sixtolab indicates an exposure time of 3.2 sec in the center and 4 to 4.9 sec in the corners.
With the large bulb of 20 Watt this is 7.3 sec in the center and 8.5 to 9.8 sec in the corners.

So the large 20W bulb gives a marginally better - more even - light spread but interestingly enough exposure times more than twice as long as the 7.5W regular size bulb!
My theory to explain this: with the large bulb only a small portion of the light flows to the mirror and condensors; the filter window is smaller than the bulb. Most of the emitted light is absorbed in the lamp house.
 

emeraldcity_grain

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Thanks Ron.
This helps expands my options as I'm finding it limited for higher wattage LED globes with higher color temp here in the States, even with Amazon.
Regards, RD
 

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Interesting thread. A point that IMHO should get more attention is that LED bulbs differ widely not only in their spectral distribution but also in the directional distribution of the light output. Some bulbs emit their light mostly in a very restricted area of around 120 degrees, others are wider and some reach 320 degrees, similar to an incandescent lamp. I assume this is critical for using the bulb in a condenser lighting system. If the light output is concentrated in a small area below the lamp, directed towards the condenser, this will make the lamp more efficient but is also likely to create more problems with uniformity. With that in mind, it would be interesting to not only know the color temperature/spectral distribution of LED bulbs that work in a given system but also their light distribution.
 

baachitraka

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Would opal around the LED distribute light evenly around all directions?
 

mnemosyne

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baachitraka,
I would guess that a matte/frosted glass globe is a prerequisite. Putting an Opal globe around the LED globe (if I understand you correctly) might indeed help diffuses the light more evenly, but I have no idea. You have to be careful not to obstruct the heatsink area of the LED bulb. As an alternative one could add a sheet of frosted glass in the filter drawer? The recent filament type LED bulbs are obviously not very suited, I have some at home in use and even frosted type projects a (although rather diffuse) image of the filament on the illuminated surfaces.

There is a German electronics dealer (www.elv.de) who do their own testing of LED bulbs and publish detailed data sheets incl. spectral data and light distribution for some of the LED bulbs they are selling.
For example if you compare two Osram bulbs from the same product line "LED Star Classic A 4000K", one 9 watt rated, the other 14.5 watts, the spectral data is quite close, but the light distribution differs considerably (110° vs. 202°):
https://files.elv.com/Assets/Produkte/11/1199/119947/Downloads/119947_lampe_mp.pdf
https://files.elv.com/Assets/Produkte/12/1269/126926/Downloads/126926_lampe_mp.pdf

Also, some LED bulbs like the two posted here, are rather long compard to normal bulbs, so this might place them closer to the condenser system which again might have influence on the evenness of the light distribution
 

baachitraka

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My condensor enlarger have frosted glass in front of the bulb but I will measure the length of original bulb and see whether LED bulbs fits.

Mine is old Durst M600 enlarger that have 75W bulb, which is giving long exposure times. So I am looking some high power bulbs that don't consume lot of current and generate heat.
 

MattKing

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baachitraka said:
Mine is old Durst M600 enlarger that have 75W bulb, which is giving long exposure times.
Click to expand...
IIRC, the Durst M600 depends on a mirror to direct the light. Check the mirror to see if it is the problem.
 

mnemosyne

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I don't have personal experience with the M600 but 75 Watt doesn't sound awfully bright, the condenser system of the Magnifax 4 (6x9) and it's smaller brother Opemus 6 (6x6) use 150 Watt opal bulbs and when exposing graded paper (= no contrast filters involved) I find the exposure times to be quite a bit longer when compared to the Color 3 halogen light head, which uses the common 12V/100W projector lamp.
 

mnemosyne

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In the meantime I did some tests with an LED bulb (Osram LED Star Classic A cool white 4000K) in my Meopta Magnifax (6x9 condenser system). The paper used in the test was Fomabrom Variant and Fomatone MG. The Osram bulb is rated at 100 watts (1500 lumen). Compared to a 150 watt tungsten opal bulb the LED bulb is a full stop faster/brighter. The contrast range that can be achieved is identical (I used a set of generic variable contrast filters #0 to #5). Some notable differences: Contrast at the extreme end of the contrast range is identical, but with the #5 filter, the LED bulb is an additional half stop faster (1.5 stops altogether). The mid range grades are somewhat shifted, the contrast of the #2 filter when exposed with the LED bulb falls in between #2 and #3 when exposed with the tungsten bulb. I did some further tests to check falloff and evenness of illumination with the LED bulb. I could not detect any problems.
 
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