The LCD shutter is a wear item with a 250 to maybe 500 hour life. 8 months of "almost non-stop" printing would equal 5760 hours (8*30*24). 5760 / 500 (hours/LCD) = 11.5 screens--so you're doing pretty good to have only gone through 4 in eight months of almost "non-stop" printing.
OTH, Printing 8 hours per day (still a LOT of printing) for 8 months = 1920 hours. 1920 / 500 = 3.8 LCDs; so I'd bet you are actually printing 8 hours/day or so and your LCD working life is normal.
These are not technically "burn" spots, but rather "worn-out" spots.
To somewhat oversimplify the issue; normally the liquid crystal molecules in each pixel in the display are chosen to have a "parallel" relaxed phase that does not re-orient the polarized light that has passed through the first polarizing layer of the LCD assembly blocking it from passing through the second polarizer (placed at 90° relative to the first)-- causing them to appear "dark"--as the curing light has been blocked light from passing through the second polarizer layer.
When an electric field is applied to "excite" a properly functioning pixel the molecules of its liquid crystal are "twisted" relative to the field; causing the polarized light to be re-oriented and able to pass through the second polarizing layer; making the affected pixel appear "light".
Unfortunately over time the relatively bright near UV radiation from the curing lamp hardens the "liquid crystal" pixels of the shutter, locking them into their unexcited parallel molecular structure . Without the first layer polarized light being "twisted" it can no longer pass through the second polarizing layer, this creates the dark pixels.
Also it seems that damaged pixels often "infect" their neighbours, causing round clusters of dead pixels to appear quite rapidly over a span of just hours.
This is not any shortcoming of the LCD screen chosen by Elegoo, it is a limitation inherent to this technology. All SLA LCD based printers suffer from this issue. It is one reason why The 405 nm near-UV wavelength light was chosen. "Nastier", shorter wavelength true-UV radiation and appropriate resin would likely shorten print times--but at the expense of accelerated degradation of the LCD.
Compromise is one of the "sucks" parts of real life.
We are fortunate that the shutters for our machines areas inexpensive as they are ($30 w/ shipping from Amazon Prime).
OTH, Printing 8 hours per day (still a LOT of printing) for 8 months = 1920 hours. 1920 / 500 = 3.8 LCDs; so I'd bet you are actually printing 8 hours/day or so and your LCD working life is normal.
These are not technically "burn" spots, but rather "worn-out" spots.
To somewhat oversimplify the issue; normally the liquid crystal molecules in each pixel in the display are chosen to have a "parallel" relaxed phase that does not re-orient the polarized light that has passed through the first polarizing layer of the LCD assembly blocking it from passing through the second polarizer (placed at 90° relative to the first)-- causing them to appear "dark"--as the curing light has been blocked light from passing through the second polarizer layer.
When an electric field is applied to "excite" a properly functioning pixel the molecules of its liquid crystal are "twisted" relative to the field; causing the polarized light to be re-oriented and able to pass through the second polarizing layer; making the affected pixel appear "light".
Unfortunately over time the relatively bright near UV radiation from the curing lamp hardens the "liquid crystal" pixels of the shutter, locking them into their unexcited parallel molecular structure . Without the first layer polarized light being "twisted" it can no longer pass through the second polarizing layer, this creates the dark pixels.
Also it seems that damaged pixels often "infect" their neighbours, causing round clusters of dead pixels to appear quite rapidly over a span of just hours.
This is not any shortcoming of the LCD screen chosen by Elegoo, it is a limitation inherent to this technology. All SLA LCD based printers suffer from this issue. It is one reason why The 405 nm near-UV wavelength light was chosen. "Nastier", shorter wavelength true-UV radiation and appropriate resin would likely shorten print times--but at the expense of accelerated degradation of the LCD.
Compromise is one of the "sucks" parts of real life.
We are fortunate that the shutters for our machines areas inexpensive as they are ($30 w/ shipping from Amazon Prime).
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