samw47•2mo ago

My emulsion burned out in 45 seconds flat last night...

I set my timer for 120 seconds like always with my 500W halogen, but the design washed out completely and I realized the bulb was way too close after measuring at 8 inches instead of my usual 14. Been seeing posts where people say closer is faster but nobody mentions how much it changes your timing, has anyone else wrecked a screen by assuming distance doesn't matter that much?

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brookep272mo ago

Saw a video from that screen printing guy on YouTube where he tested this exact thing with a lux meter. He found that moving from 14 inches to 10 inches cut his exposure time by almost 40% because of the inverse square law with light. So going from 14 to 8 inches like you did is probably way more drastic than people realize. 45 seconds sounds about right for that distance honestly, I almost cooked a screen last month by guessing instead of measuring.

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aaronlee2mo ago

I get what you're saying, but I think the inverse square law gets thrown around too much without figuring in the actual reflector and bulb setup. Those cheap units with aluminum reflectors don't focus light like a point source, so it's more of a guess anyway. Testing with a lux meter is fine for your own setup, but trying to apply that math to someone else's random rig is sketchy. The distance change is real, but the percentage drop depends a lot on how your light is built. I've run the same test with a cheap halogen setup and got way less than a 40% change because the reflector spread the light weird. So 45 seconds might work for some, but it's not a universal rule.

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