Light Intensity EV Changes not Visible at Low Values

Development Pipeline & Plugins
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1

Hey Epic,

Changing PointLight, SpotLight and RectLight Intensity value with Intensity Units=EV in a low range such as from 0.1 to 0.05, or 0.01 there is no change in intensity that can be observed. Changing to 0.0 does result in black.

This behavior does not happen with other light units such as Candelas. We are using EV for all of our projects and would need the intensity to change in low ranges.

Could you please look into this?

Thank you

PointLight with intensity 1.0:

[Image Removed]

0.1:

[Image Removed]

0.01:

[Image Removed]

0.0:

[Image Removed]

2

Steps to Reproduce

  1. Unzip and load ev_lowvalues project
  2. Load the level Content\ev_lowvalues\L_ev_lowvalues
  3. Change the PointLight Intensity value from 0.1 to 0.05, or 0.01. Observe no change at all
  4. Change the PointLight Intensity value to 0.0, observe it turns black.
3

Hello,

Thank you for reaching out.

I’ve been assigned this issue, and we will be looking into the EV brightness behavior for you.

4

Hello,

Unlike Lumens or Candelas, EV uses a logarithmic scale. The lower the value of EV gets, the less a fixed step changes the brightness.

Mathematically, 0 EV should equal 1 Candela. However, Unreal Engine 5.5 and below have a bug that did not allow for the zero and negative values for EV intensity units. This was updated for 5.6, in CL: 41454830 on //UE5/Main.

If you backport this update, you can get continuously dimmer lights by setting the intensity to a negative value, with the units set to EV.

For more information on the calculation, please see “UPointLightComponent::ComputeLightBrightness()” from PointLightComponent.cpp.

Please let us know if this helps.

5

Hi Stephen,

Thanks for the answer and the commit, we’ll take a look.