Diffuse Reflection Puns

Just took a laser show safety class, and I have to say it left me with a couple more burning questions than I went in with (pun intended). The one in particular that’s been keeping me up at night is the instruction to avoid terminating a Class 4 beam where the audience can see it, because the laser spot itself is a diffuse reflection hazard that can cause eye damage.

Needless to say, every laser show I’ve ever been to has terminated their beams on the rear walls of the venue, and provided no instructions to the audience to not look at at it. I have to assume that they’ve done some safety calculations to ensure that the beam spots are far enough away from the audience to not cause damage.

What are those calculations exactly, and how do you make them work? I understand the concept of the Nominal Ocular Hazard Distance, and I know how to calculate that. However, as I understand it, that only applies to direct beam viewing. Is there some sort of attenuation factor I can apply to that number to figure out the distance at which diffuse reflections are hazardous?

Givens are laser power in watts, laser beam divergence in milliradians, total reflectivity of the surface on a scale of 0-1, the distance between the laser source and the target, and the distance between the target and the viewer or point of measurement.

I’m trying to determine safety distances for viewing Class 4 laser beam spots on diffuse surfaces, and having a hell of a time doing it. Ideally I would be able to plug in an MPE for irradiance (like 2.54 mW/cm^2), a laser power (like 5W), a reflectivity percentage (say 10%) and a distance to the target (say 10 meters), and get out a distance beyond which viewers will not experience the MPE of irradiance upon looking at the laser dot.

Do you guys have any idea how I might go about doing that? Any help is vastly appreciated!

Edit: assume a worst case reflection angle of 0 degrees.

https://preview.redd.it/vhn9ycgr0ke71.png?width=960&format=png&auto=webp&s=38a83c7853d74ee8142695b976e4cd47295b469d

Hi everyone! I've been trying to export this render, and I'm running into a few issues in using a multi-pass render, particularly in the diffuse/reflection layers. I'm just using the standard renderer here, and in my settings, I have Straight Alpha checked, Anti-Aliasing set to Best, and Filter set to Gauss (Animation).

Just wanted to ask a few questions:

- Why are the reflections and diffuse off-kilter, and how can I fix it?
- How can I render materials in a background object? The gradient was supposed to be a sky in a BG object, but I instead put it as a separate photo in AE

Thanks in advance for the replies! :)

I’m trying to achieve a specular reflection on resin parts for a Uni Project using Stardust colours Chrome Spray Paint. I sanded the part down with micromesh then applied a Black Laquer undercoat using a spray can, as recommended and also from StarDust Colours. This achieved a nice smooth, hard glossy undercoat. (See picture 1)

I then applied a chrome paint following the instructions on line - Shake the aerosol vigorously for 10 minutes, Apply 5 ultra thin layers with 2 min intervals, dry 24 hours minimum. However the end result after a 24 hour drying period is rough, with a diffuse like reflection(See picture).

Following the advice on their website(link) I am going to try this again, but allow the paint black undercoat 3 days to dry over the weekend. I know this spray works, I was able to get a god reflection on Polsihed glass substrates instantly. Any tips or advice on how to best get a reflective surface?

Link: https://www.stardustcolors.co.uk/chrome-paint/686-chrome-spray-paint.html#/450-chrome_spray-jaune_ral_1026

Picture 1

Picture 2

Okay, please bear with me and excuse my so-so understanding of the matter at hand.
Say, we have a light source that is far, far away (light rays are parallel) and this light source illuminates everything evenly at 1000Lux/m**2. ( I assume we can pretend for the sake of the example that the third variable of distance, as in lux per square meter at X meters, isn't relevant since we're pretending that quadratic falloff isn't much of a factor due to the distance from the light- source )
Now, next to us there's an ideally matte (Lambertian reflectance-type), white* surface, that is flat and is oriented so as to perfectly face our light source.
Now my question is what is the illuminance in Lux/m**2 of that surface?

There was a fairly technical rendering tutorial where the instructor claimed that approximately 90%
of the brightness (of the light source) is 'lost' when it's diffusely reflected by a Lambertian surface.
Now, supposedly his father-in-law is a physicist, but I just wanted to get an explanation/ confirmation
that this is the case.

*white: basically has a high radiant exitance if that was the correct term, very little light is absorbed.

Again, my apologies if I've screwed up the terminology and such, I'm just a humble
paint(albeit digital)-splashing person that is trying to wrap his head around some
concepts so that I can use them practically. Also, if my butchering of the material has
made the question unclear, please feel free to ask any additional questions.

https://imgur.com/vLvslcr

Since I was disappointed with both the ambient lighting features the engine offers out of the box (flat ambient or the excruciatingly slow baking), and HDRP (10 seconds to enter play mode, really?), I started to look for ways to extend deferred rendering.

I found the "Deferred Reflections" shader in project settings (under Graphics) so I decided to try to replace it to apply some diffuse lighting in addition to specular lighting.

Needless to say, the plan was a success (image above).

Here's the diff (based on 2019.1.4 built-in shader DefaultResourcesExtra/Internal-DeferredReflections.shader source):

diff --git "a/Internal-DeferredReflections.shader" "b/DeferredReflectionsExt.shader"
index 82e1eff..3be564f 100644
--- "a/Internal-DeferredReflections.shader"
+++ "b/DeferredReflectionsExt.shader"
@@ -1,6 +1,6 @@
 // Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)
 
-Shader "Hidden/Internal-DeferredReflections" {
+Shader "Overrides/DeferredReflectionsExt" {
 Properties {
     _SrcBlend ("", Float) = 1
     _DstBlend ("", Float) = 1
@@ -73,16 +73,17 @@ half4 frag (unity_v2f_deferred i) : SV_Target
     Unity_GlossyEnvironmentData g = UnityGlossyEnvironmentSetup(data.smoothness, d.worldViewDir, data.normalWorld, data.specularColor);
 
     half3 env0 = UnityGI_IndirectSpecular(d, data.occlusion, g);
+    half3 diff = DecodeHDR(UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, data.normalWorld, 5), unity_SpecCube0_HDR);
 
     UnityLight light;
     light.color = half3(0, 0, 0);
     light.dir = half3(0, 1, 0);
 
     UnityIndirect ind;
-    ind.diffuse = 0;
+    ind.diffuse = diff * data.occlusion;
     ind.specular = env0;
 
-    half3 rgb = UNITY_BRDF_PBS (0, data.specularColor, oneMinusReflectivity, data.smoothness, data.normalWorld, -eyeVec, light, ind).rgb;
+    half3 rgb = UNITY_BRDF_PBS(data.diffuseColor, data.specularColor, oneMinusReflectivity, data.smoothness, data.normalWorld, -eyeVec, light, ind).rgb;
 
     // Calculate falloff value, so reflections on the edges of the probe would gradually blend to previous reflection.
     // Also this ensures that pixels not located in the reflection probe AABB won't

You may need to adjust the LOD value above in case it is rendered too blurry, or too watery.

P.S.

1. The original sha

I've been playing around with lasers and polarizers lately and am trying to understand the following scenario:

When I shoot a laser with polarized light at a mirror, the specular reflection keeps the same polarization (except mirrored). I can take another polarizer and block the reflected beam from the wall near the mirror wall if I rotate it properly.

However, if I take that same beam, point it at a white wall and then look through an additional polarizer; no matter how I rotate the additional polarizer I always see the diffusely reflected light. If that light maintained its original polarization, shouldn't there be a certain angle of rotation of the additional polarizer that would block my eye from seeing the reflection?

I watched some videos talking about how reflection was an electron absorbing a photon and re-emitting it. If that is correct, what about a smooth surface like a mirror makes an electron emit the light with the same polariztion?

P.S. I have virtually no background in physics, so I might be asking questions way out of my league of understanding...

According to the standard laser class system and safety guidelines, class 4 lasers (above 0.5 W) are a diffuse reflection hazard. I must be missing something, because both the radiance and irradiance of even a 10 W laser's diffuse reflection is no more than that of a standard 60W incandescent (~10 W in the visible range), which also emits uniformly in all directions. What am I missing? A 10 W laser is universally seen as an acute diffuse reflection hazard. Note that I don't think it can have anything to do with the coherent nature of laser light because the coherence is lost in a diffuse reflection.

(Note: I posted this question in /r/lasers yesterday but haven't gotten any responses over there)

So I have downloaded some nice HDRis to use in my project, but when I enable them everything is blue (clear sky HDR) or everything is orange (sunset HDR).
It doesnt look realistic at all when the room I created is all blue during the day. Of course the atmosphere should change but it looks like it is just too much.
How can I control the hue/saturation of the light (not the background image) ?

I just noticed that the entire underside of my aluminium MacBook Pro, which normally reflects light diffusely, gives specular reflections if you look in a direction almost parallel to the surface. The transition between diffuse and specular is fairly rapid and occurs around an angle of 75º (very rough guess) with the surface normal.

I'm curious as to what causes this angular dependence and whether it has a name so I can look more into it. Thanks.

Now before you ask - yes I have tried the subscription advantage pack with the Scene States but first of all it crashed 50% of the time and secondly it apparently does not recognize value changes in VRay-properties. I am rendering with VRay so that is a must. For clarification: I do NOT talk about passes here like the diffuseFilter, Reflection et cetera but rather about layers as in Foreground, Background, Characters, and anything related (extra Fog pass for characters etc)

According to the standard laser class system, class 4 lasers (above 0.5 W) are a diffuse reflection hazard. I must be missing something, because the irradiance of even a 10 W laser's diffuse reflection is no more than that of a standard 60W incandescent (~10 W in the visible range), which also emits uniformly in all directions. What am I missing?

I just noticed that the entire underside of my aluminium MacBook Pro, which normally reflects light diffusely, gives specular reflections if you look in a direction almost parallel to the surface. The transition between diffuse and specular is fairly rapid and occurs around an angle of 75º (very rough guess) with the surface normal.

I'm curious as to what causes this angular dependence and whether it has a name so I can look more into it. Thanks.