For things with a relatively great brightness and relatively small size, such as flames, light bulbs, etc., I recommend that you use a combination of a point light (set to inverse square attenuation) with IDL using an ambient mesh item. 

     But...   For things which are intensely bright relative to their size, Firefly's IDL will not react in correct proportion.  Look at the render with the ambient of the flame set high;  nothing but a flat white silhouette.  So, try giving the visible flame a gentle ambient (0.67 or so) and using an emitter prop which remains unseen but has very high ambient (Firefly seems to top out at about ambient=32).  I also like to have another prop with a softened shape surrounding the flame which will provide that "glow" effect.

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"Harley" plushie by Littlefox at RDNA

"Noel tree" by Pretty3D at R'osity  (IDL kit by me)

"MyLantern" lantern 8 by Judibug at R'osity (IDL kit by me)

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5