DIY 31 Megapixel Enlarger

Ethan Brossard said:

My screen is working fine now, so eventually yours should go back to working. When mine got burned in, I think I had it running for 12 hours or so unattended, and I think it took a couple days to get the effect to dissapear.

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Yeah it's strange, when I do these exposure tests it's only getting a maximum of about 45 minutes operation with the image displayed, then I turn it off.

This ghost effect would be pretty catastrophic in their intended use (SLA 3D printers) so I wonder how they avoid it? I'm thinking that the exposure time of each layer is probably only a few seconds and they probably blank the screen between each exposure, so the constant cycling of pixels might prevent them from getting stuck.

I could probably implement this in my code too, just have the screen flash to black and then back to the image every 5 or 10 seconds during the exposure. It would increase the exposure time, but not by a huge amount of the black screen is only displayed for a fraction of a second.

I’m guessing in SLA printers since each layer is a different shape no single frame gets displayed for a long enough duration for it to burn in. I made a gif which flashes between black and white that I set to full screen whenever I’m not exposing, and since creating that I’ve not had any issues with it burning in again.

AndrewBurns said:

Yeah it's strange, when I do these exposure tests it's only getting a maximum of about 45 minutes operation with the image displayed, then I turn it off.

This ghost effect would be pretty catastrophic in their intended use (SLA 3D printers) so I wonder how they avoid it? I'm thinking that the exposure time of each layer is probably only a few seconds and they probably blank the screen between each exposure, so the constant cycling of pixels might prevent them from getting stuck.

I could probably implement this in my code too, just have the screen flash to black and then back to the image every 5 or 10 seconds during the exposure. It would increase the exposure time, but not by a huge amount of the black screen is only displayed for a fraction of a second.

Click to expand...

The problems they met in 3D printing can be seen in this video:
TL;DR: The first layer printing takes too long time, and the heat from resin curing cannot dissipate, making the screen more prone to burn-in with fixed image at high temperatures.

Although your machine doesn't directly cure resin on its surface, it has significantly higher UV power and runtime than typical 3D printers(350w vs 50w, 1000s vs 50s), while the LCD screen absorbs over 80% of the UV power. I know you've measured the temperature, but I'm still concerned about whether some localized heat points may appear and pixels might overheat. Maybe you can try not only have the screen flash to black(now they absorb all the UV power!), but also cut off UV LED for a while.

Yezishu said:

The problems they met in 3D printing can be seen in this video:
TL;DR: The first layer printing takes too long time, and the heat from resin curing cannot dissipate, making the screen more prone to burn-in with fixed image at high temperatures.

Although your machine doesn't directly cure resin on its surface, it has significantly higher UV power and runtime than typical 3D printers(350w vs 50w, 1000s vs 50s), while the LCD screen absorbs over 80% of the UV power. I know you've measured the temperature, but I'm still concerned about whether some localized heat points may appear and pixels might overheat. Maybe you can try not only have the screen flash to black(now they absorb all the UV power!), but also cut off UV LED for a while.

Click to expand...

Yeah I thought that screen temperature could also be a reason that I see this issue faster than people using the same screen for normal enlargers with far less optical power.

I did measure temperature on the LCD using a thermocouple during development and I've aimed to keep steady-state temperature under 70 degrees Celsius. One difference with my setup vs. a standard SLA printer is that I have an enormous amount of cooling air blowing over both sides of the LCD screen constantly during operation (without that, the LCD would overheat and fail within seconds I suspect).

I'm not convinced that a black screen will get appreciably hotter than a completely 'clear' screen. You have to imagine that the maximum transmission of UV light through these LCD screens is <5%, that means even when the screen is completely clear it still absorbs 95% of the light energy hitting it. So the difference in heating of a completely black screen vs. a completely clear screen is less than 5%.

I could turn the LED on and off during operation, which I suppose would just reduce the average power and thus average temperature of the LCD during operation (resulting in longer exposure times but at a lower temperature). In some ways this is functionally the same as running the LED at a lower continuous power, which I can also do as it's connected to a variable constant-current power supply. One difference in operating at a higher peak power with some cool-down time vs. operating at a continuous lower power is the higher peak-power operation should be better for processes that have non-linear sensitivity to light (like DAS sensitised gelatin, which hardens via a two-photon process and benefits substantially from higher exposure power over shorter times).