@I14R10 (I14R10) posted a new topic, subject "Are Lights the same as light emitting materials?". It read:

   Hi, Blender newbie here, but I have experience in other 3D programs.  
    I know that in 3ds max light emitting materials doesn't produce the same results as real lights. Is that the case in blender?

After which, @howtoblend (howtoblend) added

    Welcome to the community!
    
    3 main differences:
    
      1. Realistic reflections
    
      2. Strength considerations
    
      3. Shadows
    
      4. Emissions from meshes are reflected as the shape of the mesh. Points, spotlights and sun lamps are just round spots. If you modeled an actual lamp, the lightbulb mesh set to emit would appear more realistic than a point lamp.
    
      5. A mesh emitting light calculates strength by area of the mesh (watts / meters^2). Points and spots are also measured in watts. The sun lamp (and hemi which cycles treats as a sun lamp) is overpowered since the actual sun emits about 4 * 10^26 Watts but that would be ridiculous to type in every time. The strength setting was simplified and a value of less than 5 is best. The sun casts rays evenly in the direction you point it on the whole scene so it is simpler than scaling up a giant plane to fill the sky. Also note, that if you increase the size (not scale) of a lamp the scene will get darker since the light has a larger surface area but the same wattage. It's useful to increase the size to get softer shadows but you'll need to increase the strength too.
    
      6. Only shadows cast by lamps appear in the shadow pass of the compositor. Shadows can be removed based on objects using the ‘ray visibility' setting only with lamps. You can limit the number of bounces for each lamp individually as well.
    
    
    
    
    There are other differences too but these are the big ones. Hope that helped. Cheers!
    
    P.S. - Props to the cycles encyclopedia ebook. Most of this knowledge can be found there.

So @Ace_Dragon (Ace Dragon) replied

    Another thing is that the standard lamp types tend to make use of better sampling algorithms due to them being having a defined size and behavior (so light from them will converge faster even though the final result would be more or less the same as from a emitter).

After which, @I14R10 (I14R10) added

    Thanks guys. One more question. When using glossy shader I can't adjust the sharpness of the reflection. I can only adjust roughness and that's it. How do I do that?

After which, @sundialsvc4 (sundialsvc4) added

    Also bear in mind that _rendering algorithms_ can be _fundamentally_ different from one another! Consider, for example, the differences between Cycles and Blender-Internal: probably the most basic difference between the two is their respective treatment of “what is ‘a light source?'” And, the reason for this difference goes all the way back to the fundamentally-different approaches that these two take, to what is otherwise “the same problem.” Direct comparisons between the two have no meaning.
    
    For example, in BI, a light-emitting material might “glow in the dark,” but it won't be lighting-up things nearby. (Unless you also put a Lamp in it.) Cycles looks at things completely differently, because it _works_ completely differently. So, when discussing topics like these, be careful to remain within the context of (any …) _one_ renderer, lest you compare apples to oranges.

To which @Richard_Marklew (Richard Marklew) replied

    > For example, in BI, a light-emitting material might “glow in the dark,” but it won't be lighting-up things nearby.  
    >  It can but the light will not cast any shadows

To which @howtoblend (howtoblend) replied

    > Thanks guys. One more question. When using glossy shader I can't adjust the sharpness of the reflection. I can only adjust roughness and that's it. How do I do that?
    
    Roughness is sharpness. If you put roughness at 0, it will result in a perfectly clear reflection. If you want to have sharpness and roughness, try mixing two shaders (typically diffuse and glossy) with a mix node.
    
    Good luck, have fun!

Then @I14R10 (I14R10) said

    I see, thanks! A bit different than 3ds max, but when you figure it out you can do the same.

So @Andr3yAngel (Andr3yAngel) replied

    I also come from using 3DS Max. Now i`m using Blender for more than 3 years and i find difficult to get to max, after working with Blender. Blender it`s just…more quicker and more easy to understand. In terms of rendering the most useful feature from Blender is the viewport realtime render. And that`s my opinion  have fun dude!

@Roken (Roken) replied

    For glossy, don't forget that you can mix glossy nodes, so you can effectively put a topcoat on a roughly blurred surface without having to layer materials. very handy for painted surfaces, for example.

@sundialsvc4 (sundialsvc4) replied

    Richard Marklew:
    
    > It can but the light will not cast any shadows
    
    Ahh, I stand corrected.


{'source': 'discourse', 'url': 'https://blenderartists.org/t/are-lights-the-same-as-light-emitting-materials/657063', 'title': 'Are Lights the same as light emitting materials?', 'views': 1395, 'has_accepted_answer': False, 'word_count': 790, 'like_count': 0, 'reply_count': 4, 'participant_count': 7, 'posts': 11, 'tags': '', 'author': '@I14R10 (I14R10)', 'participants': '@I14R10 (I14R10), @howtoblend (howtoblend), @Ace_Dragon (Ace Dragon), @sundialsvc4 (sundialsvc4), @Richard_Marklew (Richard Marklew), @Andr3yAngel (Andr3yAngel), @Roken (Roken)', 'image_url': [None], 'created_at': '2015-12-01T01:43:26.000Z', 'last_posted_at': '2015-12-17T19:22:27.000Z'}