Increase your projector power output by 13% with this one weird trick!

AD001AD001 Member, Backers
Formlabs hates him! Clickbait title aside...

So.. I like to tinker. I also have a G&R Labs Model 221 light meter (http://www.grlabs.com/uv-light-meters/meters/model-221/). I calibrate my printer every few months by dividing my build area into 15 test points. I was watching Garage Science's mirror replacement video re: UV pass filter (will discuss later) and it got me thinking: Is there ANYTHING I can do to bump this performance up without modding my machine further? For the record, my projector is a Viewsonic PJD7822HDL and I love it.

Turns out... yes there is! After an hour or two of tinkering with settings, I have found that adjusting the color temperature of my projector yields an average of 13% light intensity increase (as measured in mW/cm^2 @ 405nm) across my 15 test points.

To lay some numbers down, with a build area of 170mm x 94mm (roughly), I was averaging 8.81mW/cm^2 4 months ago, 8.54mW/cm^2 before fiddling, and 9.63mW/cm^2 after, at an 'equivalent lamp hours' of 690.
To note: my projector varies a TON across the build area. I tend to print in a 75mm x 100mm portion of my full build area that sits around 11mW/cm^2 @ 405nm. Also, I have no idea what an "equivalent lamp hour" means. It's a Viewsonic thing.

So, what did I actually do? Well, after tinkering with every setting I could find, I noticed that setting a "custom" profile to the "PC" settings and adjusting color temperature from "T2" (default) to "T1" is all it took. I suspect the temperature nomenclature will vary from projector to projector, but the important bit is this: Your projector, due to stock settings, is likely intentionally kicking out a notable amount less of relevant curing light than it could be. The color of your input light doesn't matter here - white is best for this... the projector takes the input, adjusts it, and throws it. 

TL;DR: I increased my projector output at relevant curing wavelengths by roughly 13% by changing color temperature from T2 to T1, with "PC" display settings. While I did not technically increase the amount of blue-ish light the projector COULD output, I found that by default it was setup to not actually kick out all that it was able to do in the first place.

Oh, and because I said I'd discuss it... The Garage Science  video I was talking about relates to installing a UV-pass filter ( check him out if you don't know him already, he is on the forums too I believe). The mirror he recommends is a UV-pass filter (https://www.pnta.com/lighting/dichroics/rosco-permacolor-dichroic-filter-3660-double-coated-uv-pass/), but I'm considering going for their slightly-greater-allowance "deep purple" version (https://www.pnta.com/lighting/dichroics/rosco-permacolor-dichroic-filter-4200-deep-purple/). I presume he picked the UV-pass due to its sharper cutoff on the lower (and more damaging to DLP chips) wavelengths... but if he/you read this, I'd love to hear more info on your decision.

Anyway, that's that. All the best!

Comments

  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer

    AD001,

    So you went to a higher Kelvin color temp, which favors the blue side of the spectrum and you saw that much increase of 405 nm with your meter? That is good to know!

    The DLP projector is a curious thing. You have a light source that emits a wide range of wavelengths on one end and a DLP chip with mirrors on the other. The two things in between that impact that are the glass filter on the lamp and the color wheel. In this case, by switching to a cooler color temp, you are favoring the blue end of the spectrum over the red end and the mirrors are reflecting more light when the wheel is in the blue and white regions than the red or yellow regions (can't remember the actual color scheme of the color wheel in the Acer/Viewsonic projectors).

    The other control we should also look at is brightness, since that adjusts intensity as well, but too much brightness can have a negative impact on (over)curing and print accuracy.

    I wish I had one of those meters - I can't justify the cost. ;-) I used Gravelle's tool to create a custom mask using the photoresistor method. I do need to go back and adjust it, but it has worked well for me. :-)

    Regards,
    Ron

    Ron
  • Joseph_OsbornJoseph_Osborn Member, Backers
    @AD001 that is a cool discovery! What change did you make to your exposure times after changing the projector color setting? Are we talking 5 seconds down to 4.5 seconds? I have a PJD7820HD and it should have the same setting.
  • AD001AD001 Member, Backers
    edited February 9
    Ron,

    I looked into adjusting the brightness / contrast, but the results were disappointing. For that experiment I had the projector focused on the wall (so I could actually read the menu text!) out of the printer and had a checker-pattern projected. I don't remember how large the projection area is -- it's unimportant. All testing was done between two specific points to eliminate variability. The projector has a color preset called "brightest" as well, which locks all the other color adjustments to something specific, which was also tested.

    Baseline power in black area: 0.00mW/cm^2
    Baseline power in white area: 0.71mW/cm^2

    "Brightest" preset power in black area: 0.00mW/cm^2
    "Brightest" preset power in white area: 2.90mW/cm^2

    Max brightness / contrast adjustment power in black area: 2.43mW/cm^2
    Max brightness / contrast adjustment power in white area: 2.96mW/cm^2

    Color Temperature adjustment power in black area: 0.00mW/cm^2
    Color Temperature adjustment power in white area: 3.06mW/cm^2

    So, based off of my data... not only does adjusting the color temperature provide an increased bonus above adjusting brightness, adjusting the brightness above baseline appears to be a REALLY bad idea, even if playing with contrast! It is very difficult to distinguish the light from 'dark' areas when brightness is high, as the numbers back up. The ambient light in black areas leaves 0.00 fairly quickly when brightness is increased, so I'd advise keeping it static.
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    edited February 9
    I would be curious to know what the largest brightness setting would be before you started to see the side effects of reflection inside the light path? That would be the optimal brightness setting. Contrast would need to be situated as well since it will have an impact on the black level of the output.

    Glad to see someone taking the time to find the optimal settings - thanks! :D
    Ron
  • AD001AD001 Member, Backers
    Ron,

    I'm on the road at the moment but will check when I get home in a week or so. What I can say from observation is that it didn't take much above the default brightness/contrast settings to start seeing negative effects. Given that changing the color temperature had a notably more pronounced effect than maxing the brightness, I'm not sure that further adjusting the brightness and finding an 'optimal' setting would be a worthwhile amount in any case maybe 2-4% more power max and you'd still take a tiny bit of reflection hit is my hunch... but I will check!
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