Exposure amount vs Exposure time question


Just asking for a ‘sanity check’

Example 1:
Exposure time = 5.0 sec
Exposure amount = 100% (pure white in the PNG image)

Example 2:
Exposure time = 10 sec
Exposure amount = 50% (50% grey value in the PNG image)

Are these two examples really equal, or is there something else to consider such as light bleed, cure depth, photon reaction, etc…

What I am wondering is if the layer is thick enough, won’t the resin closest to the DLP get the most light, and at some point these two examples don’t really match. Would the 100% will have a deeper initial penetration depth and actually be able to cure thicker layers… OR the 50% might not cure the resin closest to the glass as fast and thereby still achieve the same result???


Also, Using the examples above:
If I create a file with a series of squares and vary the grayscale amount, would the 50% grey squares be exactly equal to an exposure time of 2.5 seconds - or only a rough approximation?


Resin curing is dependent on the dose (intensity over time), so it’s mostly equal, but not for really low intensities (i.e. 10% for 10s is not really equal to 100% for 1s). Adding @greener1 in case he has additional thoughts.


Owen’s answer is correct. The penetration depth doesn’t change (significantly) as the resin cures. But lower intensities are simply less effective at curing. See step 5 of this Instructable


I am publishing a conference paper in the coming IMECE, part of the work done on the paper was validating the grayscale colors in the PNG with the power measurement. i exposed a complete picture of different grayscaled colors and measured the the power per 1 cm2. i can assure you that the relation between the graysacle value [0-255] and the power/area (mW/cm2) is linear and the energy dosage in both cases you asked about are the same.
and actually what the grayscale value do is change the exposure time by changing the _PWM intervals of the mirrors at this grayscaled area in the png and don’t change the light color.


i was thinking about repeating the same exposure time and penetrating depth experiment using the grayscale technique as i think you are doing. your are always 10 steps ahead in this field. i like the idea.


It looks like you are the one ahead my friend! :grinning: Best of luck on your paper!

As for my recent goal - I am trying to develop a 2 step process to develop all the exposure settings for any resin. Using the working curve file is a good starting point for cure depth and resolution, but it doesn’t address the exposure time needed for adhesion and dimensional accuracy.

My current image stack takes a series of squares and varies the size and grey value between 100% and 91%. Using the layerSettings file, I am then changing the exposure time every 20 slices until the exposure time is 0.00. I am looking to quickly gain the lowest possible exposure setting for a given layer thickness and feature size based on the result of this one print.

I will still need to run this file for each layer thickness, but I am hoping to get each print in less than 30 min in an effort to reduce the amount of time it takes to develop a solid understanding of the settings needed for each resin.


Wow, very cool both of you.