A couple of folks hit me up asking me if i would share the method I use for doing the lightsabers on costume photos. Here's what I do....feel free to PM me with any questions.
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pick brush size (based on size of saber), and set hardness to 35-50% (based on the image and personal preference, you will blur later) NOTE: Line tool work fine too, will have to blur later)
create new black layer
set that layer to "screen"
paint the one line to cover your saber (or use line tool & rasterize) on the black layer (if you used the line tool, once drawn, rasterize the layer, then merge with the black, and continue)
making sure still set to screen, duplicate 5 times
The rest = math (sorry)
core = whatever size covers your blade
(Note: The layers below may not be your layer name, just simply a numbering method)
layer 1 - gaussian blur: 1-5, depending on size...this will be the white core of the finished product
layer 2 - gaussian blur: core x .5 (so if blade = 10, this will be 5)
layer 3 - gaussian blur: core x 1
layer 4 - gaussian blur: core x 2
layer 5 - gaussian blur: core x 3 or 4 (personal preference)
layer 6 - gaussian blur: core x 8
Set opacities as follows:
layer 4 - 90%
layer 5 - 60%
layer 6 - 30%
From there do Layer --> Merge Down (or CTRL+E / CMD+E) until all your SABER layers are merged into one (don't merge onto the other image layers).
Then go to image --> adjust --> color balance. Tweak settings to your liking.
Note: Red is very, very difficult to get "right." If the background is even slightly light, it will look pink. If you "hide" (click the 'eye') the image/background layer and just do the saber with no background, it will give you a better idea. For the reds, you can also try duplicating the final saber layer and play with opacities and saturation levels.