Daz Studio Watts and Luminous Efficacy

When using a mesh light and choosing watts, you get luminous efficacy as a choice. It seems to alter the amount of light put out by a certain number of watts, but there must be something else to it.

Why wouldn't you just increase or decrease the amount of watts to change the light output? Why have two settings that appear to do the same thing? 

So confused! Anybody know WATTS up with this?

yes please what the heck does that do lol... 

Haha, 'WATTS UP', I enjoyed that one.

I'm no expert at this, but efficacy, in a practical sense could help you choose an efficient light bulb when purchasing one.

Many render engines offer the control over both Luminance (W) and Efficacy, which unless the bulbs you physically intend using in your (architectural) project, specify the Efficacy value, I personally see no use for. As you would have noticed, increasing the Efficacy makes the light brighter. For rendering purposes it adds, in my opinion an unnecessary additional setting to consider/ignore, but again it can be useful if and when needed.

I personally prefer to work with Lumens (Brightness), but hey, use whatever you are familiar with.

As to your question, why indeed? But the choice is given to you to decide i.e. use a single value input or two :)

I decided to pick one and become familiar with it. What I will add is that your Luminance settings must of course be considered in conjunction with the Tone Mapping settings i.e. an EV Value of 7/8 for internal scenes or 14 - 16 for bright external scenes; give or take. In other words Photographic principles.

I'm with 3D Centric, and just because I'm in the same boat as you PsychoRobby. I just use lumens because I know what I'm going to get when I adjust the value. LOL. 

OK, thanks. That's kind of what I thought. I have been using lumens but just wanted to make sure I wasn't missing out on something. Ya know, like some cool hidden feature in Daz...

Thanks again!