Converting my Omega D-2 enlarger to LED illumination

[ASA1000]

[QUOTE=koraks;1666064]@ASA1000 if I were you I'd look into the airflow around that fan to make sure it doesn't blow any dust onto the negative stage. I'm not too concerned about vibrations; I'm running an even more challenging setup with two fairly powerful fans at pretty high speed and it doesn't cause any issues whatsoever.

I'll have to see what happens. The enlarger is grounded, the HIVAC is humidified and I exchange the air in the room every 15 minutes...... plus I have a 25 year old Staticmaster Brush!!

[stevea]

Since everyone is piling on, I'll just note that 36W at 110V is actually 300mA, not 3A, and Ohm's law doesn't really apply since this is a non-linear circuit.

But my real question is: do you notice a delay between turning the light source on and the LEDs actually lighting? LED drivers usually use switching regulators (for efficiency) and can have a delay before the output goes live - you often see this in LED downlights, incandescent replacements, etc. I'm interested in whether this happens with these special-purpose LED drivers.

thanks

[ASA1000]

Since everyone is piling on, I'll just note that 36W at 110V is actually 300mA, not 3A, and Ohm's law doesn't really apply since this is a non-linear circuit.

But my real question is: do you notice a delay between turning the light source on and the LEDs actually lighting? LED drivers usually use switching regulators (for efficiency) and can have a delay before the output goes live - you often see this in LED downlights, incandescent replacements, etc. I'm interested in whether this happens with these special-purpose LED drivers.

thanks

It seems to be instant on, but until I have some developer and run some consistency tests, I really can't say for sure. What I do know is, after the exposure, if I touch the aluminum heat sink, the leds will glow! Understand. I'm making this up as I go along. ;-)

[Tin Can]

Any LED I have used for enlarging has a delay

I have not studied incandescent, but it was common to allow the incandescent to warm up and use a shutter to control light

Not sure what your problem is

I usually add a lot of diffusion for several reasons

[tundra]

I have an ongoing interest in designing something like this. How/do you plan to control LED colors to get VC filtration? Or are you just trying to emulate an incandescent bulb color temp?

I want to build something where I control the intensity of soft light and the intensity of hard light independently and also have a focus white light position as well as an overall brightness control.

[Ulophot]

Wolf, thanks for making this. I'll show it to a friend who finally finished building me an LED head; you may have seen my posts on it, though I haven't posted images yet.

Your solution is elegant, though I sold my VC unit long ago when I got my Zone VI (Aristo-style, like yours) coldlight.

I'll be interested to hear how the light-evenness issue pans out. That's been the most significant issue with mine.

[Bernice Loui]

Few observations..

"white" LEDS (in this case 3,000K) have three individual LEDs of Red-Green-Blue inside and they are coupled to specialized phosphors to increase their light output efficiency. The trade off being the three peak light output color outputs instead of a uniform light spectrum output as would be from an incandescent, sunlight or similar light source. Humanoid eyes perceive three peaked light output from LEDs as "white" photographic materials might not record light in the same way.. This is an important consideration due to the way variable contrast B&W papers work and how contrast grade control is done with VC black and white papers..


https://www.sciencedirect.com/scienc...3107051830029X

White LEDs typically have about a 3.5 volt forward voltage to make them go.. and this voltage changes as their temperature goes up. If the LEDs are driven with a constant voltage source, the current into the LED goes up causing an increase in light output and more heat generated in the LED. This is why LEDs are driven with a constant current source to reduce this baked in problem.

"Why Drive White LEDs with Constant Current?"


https://www.analog.com/en/technical-...t-current.html

~It is also why the power unit takes time before the LEDs can be powered to illuminate them as the power source uses negative feedback and more to control the current output into the LED.

Connecting the LED array in parallel is not good. This forces the power dissipation in the power unit to be a LOT more than it needs to be and aggravates the forward voltage issues that is baked into how LEDs work. Simply wire the LED array in series to stop this problem. Check the max output voltage on the LED power unit to determine how many LEDs can be wired in series and meet the LED power unit's specifications. This might be two strings of six LEDs each instead of twelve LED in series..

12 LEDs at 3.5 volts = about 42 volts needed at the driving current of 1(?) amp..

6 LEDs at 3.5 volts = about 21 volts per 6 LED string at the driving current of 2(?) amps total into the two LED strings.

Keep in mind, current to control LED light output intensity/power, NOT voltage as this varies with each LED and operating temperature.

There will be a time delay before the power unit can make the LEDs go. There are ways to make the power unit do "near instant on" this is a design detail that required knowing how all the individual parts of the system works on their own then, designing the system to allow each individual part to work at their ideal best.


Bernice

[ASA1000]

I have an ongoing interest in designing something like this. How/do you plan to control LED colors to get VC filtration? Or are you just trying to emulate an incandescent bulb color temp?

I want to build something where I control the intensity of soft light and the intensity of hard light independently and also have a focus white light position as well as an overall brightness control.

I'm just using 3000K LEDs and I'll use filters for variable contrast.

[ASA1000]

Few observations..

"white" LEDS (in this case 3,000K) have three individual LEDs of Red-Green-Blue inside and they are coupled to specialized phosphors to increase their light output efficiency. The trade off being the three peak light output color outputs instead of a uniform light spectrum output as would be from an incandescent, sunlight or similar light source. Humanoid eyes perceive three peaked light output from LEDs as "white" photographic materials might not record light in the same way.. This is an important consideration due to the way variable contrast B&W papers work and how contrast grade control is done with VC black and white papers..


https://www.sciencedirect.com/scienc...3107051830029X

White LEDs typically have about a 3.5 volt forward voltage to make them go.. and this voltage changes as their temperature goes up. If the LEDs are driven with a constant voltage source, the current into the LED goes up causing an increase in light output and more heat generated in the LED. This is why LEDs are driven with a constant current source to reduce this baked in problem.

"Why Drive White LEDs with Constant Current?"


https://www.analog.com/en/technical-...t-current.html

~It is also why the power unit takes time before the LEDs can be powered to illuminate them as the power source uses negative feedback and more to control the current output into the LED.

Connecting the LED array in parallel is not good. This forces the power dissipation in the power unit to be a LOT more than it needs to be and aggravates the forward voltage issues that is baked into how LEDs work. Simply wire the LED array in series to stop this problem. Check the max output voltage on the LED power unit to determine how many LEDs can be wired in series and meet the LED power unit's specifications. This might be two strings of six LEDs each instead of twelve LED in series..

12 LEDs at 3.5 volts = about 42 volts needed at the driving current of 1(?) amp..

6 LEDs at 3.5 volts = about 21 volts per 6 LED string at the driving current of 2(?) amps total into the two LED strings.

Keep in mind, current to control LED light output intensity/power, NOT voltage as this varies with each LED and operating temperature.

There will be a time delay before the power unit can make the LEDs go. There are ways to make the power unit do "near instant on" this is a design detail that required knowing how all the individual parts of the system works on their own then, designing the system to allow each individual part to work at their ideal best.


Bernice

Thanks! I'm learning quick and all the information I can get is very helpfu.l

[domaz]

Anyone thought about just picking up two of the high power 100W COB units- one for Blue and one for green, then you could individually dim them via an LED controller and basically have infinite set of Multigrade "filters" and contrast controls. A lot of people are already using the UV version of these units to expose Alt Process successfully. Two 100W units are probably way overkill for Silver Gelatin actually.