High CRI LED for "Workprinter" movie transfer machine

I have a machine for transferring movie film. It is called a "Workprinter:"



and it uses a very old-fashioned, very low CRI LED as the lighting source. This low CRI rating results in colors that are not "true" compared to what I would get with incandescent or halogen lighting.

I would like to replace this LED module using a high CRI LED.

Here is a picture of the module:



As you can see, it is round (about 1" in diameter). It runs off a 5V DC supply, with a dropping resistor.

Here are my requirements:

1. High CRI (90 or higher would be nice).

2. 5V operation (I would think that most flashlight LEDs can run off 5V).

3. Built-in diffuser. As you can see, this LED module has some sort of diffuser/lens. I can easily build my own diffuser, so this one is not an absolute requirement.

I am somewhat indifferent to color temperature (this gets "zero'd out" with the camera white balance) and, to some extent, lumens, although brighter is always better.

I hope I have posted this in the correct forum.

I appreciate any ideas you can provide. Ideally, I would like to have a suggestion that includes not only the make/model of LED, but also a suggestion for a supply source.

Thank you in advance!

John Meyer

My initial thoughts:
LED: nichia 219. they can have a cri of 92+ and nice colour (4500k? 5000k?)
Driver: since it supplies 5 volts you could send that 5v to a 7135 driver that woudl in turn drive the LED. depending on which driver you sued you coudl get whatever current you needed and maybe even have some modes. depends on how professional and user friendly and idiot proof the setup needs to be.

I'd bet theres many other options and other people will offer different advice; mine is not the definitive word on this subject.

Thanks! That's a good start. I forgot to ask about a driver board since I am accustomed to the old-fashioned LEDs that just required a dropping resistor. I'll start Googling and see what I can find for a supply source.

If you want extra light, make sure to purchase the newer Nichia 219B emitters... not the older 219A.

Mountain Electronics has 92 CRI 219Bs in stock. I just built a triple with them last night. Lovely tint!

By your post I had assumed the machine had a 5 volt supply that fed the existing LED? with a buck driver (or a 7135 based unit that was well heat sinked) you could likly just use the existing 5 volt line since most power LEDs take in the 3 to 3.5 volt area

If you want to get close to incandescent lighting, the XM-L2 S6 7D3 CRI 90+ is pretty much as close as you can get in my opinion. I got mine from Illumination supply but it was the bare LED so had to reflow on to a MCPCB.

Firs of all remove that lens and let us know what LED is hiding inside, than can we talk about replacement. Otherwise it will be royal PITA to focus the beam with existing setup.

Fireclaw18 said:

If you want extra light, make sure to purchase the newer Nichia 219B emitters... not the older 219A ... Mountain Electronics has 92 CRI 219Bs in stock ...

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Very useful. I am an EE, and have accounts at Digikey, Mouser, Newark, etc., but these "flashlight LEDs" are not stocked by the usual supply houses, so the source of supply, as well as the specific LED spec, is very helpful. Thanks!

By your post I had assumed the machine had a 5 volt supply that fed the existing LED? with a buck driver (or a 7135 based unit that was well heat sinked)

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Yes, the Workprinter contains a small RS-25-5 5V, 5.0A switchmode supply that drives the existing LED (through a 5W dropping resistor), as well as a small DC motor that is used to run the converted projector at about 1/3 rated speed.

As for the 7135, since I haven't read much in the custom flashlight forum, I didn't know about that chip. I assume that it has some additional value beyond the simple one or two transistor current source that we all built in circuit labs forty years ago.

If you want to get close to incandescent lighting, the XM-L2 S6 7D3 CRI 90+ is pretty much as close as you can get in my opinion. I got mine from Illumination supply but it was the bare LED so had to reflow on to a MCPCB.

Click to expand...

It would certainly be an added bonus to have the color temperature coincide with either tungsten or daylight, because I could then just use the built-in presets in the camera. However, CRI is the key spec for this excercise. I'll check out the XM-L2. Thanks!

First of all remove that lens and let us know what LED is hiding inside, than can we talk about replacement. Otherwise it will be royal PITA to focus the beam with existing setup.

Click to expand...

I'm reluctant to do that at this point, because if my upgrade fails, I still want to be able to use the machine with the existing light.

You do realise there are only three screws to disassemble the lens part? Or am I missing something in the picture?

My small contribution :
if you're looking for a high CRI led manufacter, I would recommend you either Nichia or Osram.


At work we use mostly Cree and Nichia leds but I also had the chance to handle some Osram high CRI led and the color rendering is really excellent.
Nichia 219B R85 minimum CRI is 85 but his typical is 92 (I have the opportunity to check Nichia's production data and most of the high CRI led going out the manufactory has a CRI of 92/93)
Osram OSLON Square, OSLON SSL 80 has a minimum CRI of 90 and typical of 96. OSRAM SSL 150 exists in high CRI version and has a minimum CRI of 90 and typical of 95


Hope this will be helpful

The lens is likely not super exact in its positioning, you should be safe to carefully unscrew the self-tapping screws and get a look at the LED. The particular Nichia 219b in question is a very nice LED, and should work fine, but we would like to make sure that the LED is at the same focal point as the old LED was, and depending on the original LED, this may be easy, or you may need to use metal spacers to get the spacing just right. Sounds harder than it is.

I wouldn't even bother with a driver. Just keep using the resistor.