Guide: Calibrate irradiance without a radiometer


Irradiance is the measurement of the amount of light that shines from Ember’s DLP projector, through the tray, onto the build head. Because this light is the energy that builds your models, it’s essential that the projector is calibrated to the proper irradiance value. If this setting goes out of range, it can cause prints to fail. The easiest way to calibrate the irradiance of your projector with a given tray is to use a radiometer and follow this guide.

However, if you don’t have a radiometer, you can still check if your projector is within range by printing a special test part. This test part has tall, thin posts of varying sizes. The posts stand up straight when they receive enough light, and collapse when they don’t receive enough light. By printing the part, you can tell whether to turn your projector LED current up or down. After a few prints and adjustments, you’ll be calibrated!

Irradiance Test.3ps (741.6 KB)


  1. Download the test part.
  2. Load the test part into Print Studio or Netfabb.
  3. Choose your resin and settings.
  4. If your prints have been failing and you know you need to turn up the projector LED current, do that now.
  5. Print the test part.
  6. Inspect the test part. It should look like the pictures below:

Ideally you want 4-6 rows standing up, and the rest collapsed or missing entirely. If none of the rows are missing, your irradiance is probably a little high, but it may be fine unless you have very fine features.

Looking at the holes on the front, you should be able to see at least 9 rows of holes. If the 9th row is filled in, your irradiance is probably a little high.

Happy printing!

Resin tips

Hi Owen! What should be the printer’s profile and layer height for this irradiance test? Or any setting will do? Thanks!


Any setting that’s appropriate to your resin should work (i.e. don’t use the PR48 settings with PR57), but if you a layer thickness of more than 50 microns, the side holes probably won’t come out great.


Got it! Thanks Owen!