If the images in your Batch are too dim, you can open them in the main editor and lighten them using the Improve lighting feature. You access the main editor from the Batch Editor and when you exit, you can choose whether to apply the improved lighting to all images in your batch.
Steps (Web App)
Create a new batch, resume a previous batch, or work with the batch you already have open.
Select a dim image to open it in the main editor.
Select the foreground layer and activate Improve lighting to enhance the light in the image.
Exit the editor to return to your batch.
Choose whether to apply the changes to all images in your batch.
Learn how to use Improve lighting
Improve lighting for batch images works the same way as editing individual images outside of a batch. Learn how it works in Improve the lighting of a design (iOS) . The important difference in Batch is that that when you exit the main editor, Photoroom asks whether you want to apply your changes to all images.