Yet another person with a Lightsaber

What did you use to get the effect? What caused the hard line at the bottom?

this may not work properly for Iray, but, have you tried lowering the opacity of the blade in total? The outer edges are semi-transparent, the inner mass is more solid... maybe, try lowering opacity on that? And, raise the emissive intensity on the outer edges by a good amount... a rough guess here, but, I think that 75% of the emissive levels of the inner side should work, assuming they are all at the same opacity levels. It would be like a fake bloom effect, maybe with a touch of blur brushes later on photoshop, to hide any sharp edges.

EDIT:
ok, since it's already here, I won't upload it too... use saberlight, it's in the blog section already. Set as Poser native smartprop for V4, but, should work in Iray. Not so sure if it gets parented to the respective figure's hand at DAZ, but it DOES load. Now, the main thing to work on, is the "blade". It's 3 closed sylinders, one inside the other. Poser wise, it always needs photoshop post-edit to add the right amount of bloom effect, but in DAZ, with the appropriate built-in emissive shader, it works fine. In the following fast renders, the first two have the exact same emissive stats (very light blue emissive color, to blend with the diffuse green the ray loads with, as default, 5000 W emissive strength, and 15 lm/W) and the exact same opacity cu in each ray (o.5 opacity cut). The hilt/handle of the lightsaber is done by using various metallic and the smooth plastic iray built-in shaders, and the default emissive values on the gauge and 2 tuny LEDs. The render, at 1000 pixels sample, with no lights, and only the dome on a gray gradient on relatively low intansity, with bloom filter turned on, and off respectively, did pretty fast, hitting 96% at about 7 minutes on each of the four renders.
The first image is without bloom effect, and the second with bloom. As you can see, the bloom is too "fat", and, without it it's a glow-stick effect, no real "beam" effect.

The following two, I tried a different approach. I used half the emissive strength of ray 1 to ray 2, and half the emissive strength of ray 2 to ray 3 (ray 1 5000 W, Ray 2 2500 W, ray 3 1250 W). I also turned ray 2's opacity cut to 0.25, and ray 3's opacity cut to 0.125.
The non bloom render is a bit horrid. The bloom render however is just thinner enough compared to the above bloom render, to hit that sweet spot.

@aftyrbyrn
I just used the bloom filter in Daz to get the lighting effect
I have a few other saber props that the bloom turns out better, but they take more time to set up in the render....that was a fast 3 minute render just for example.

other Saber prop, with and without bloom effect, personally i prefer all of then with the bloom on looks better IMHO.

I know what ya mean, I've tried many times to get the bloom to look right with bright environments and you can only get so much, no matter what it always starts to blend in with the background lighting.

That's why i tend to do most renders like this in low light or minimal lighting, can take away from the render, but just one of my OCD's....LOL

Force FX Sabers here....I refuse to grow up, well to a point...LOL