This can be done with static prop models, using two models and a little bit of trickery, as I did in both my TWHL Tower map and the christmas tree decorating minicompo that Captain Terror hosted last year.
You'll require two models. One of them is the base model:
And the other is the glow model:
They should be placed that the glow model sits around one Hammer unit away from the base model. If the model is designed to be viewed from a distance then you might want to increase the distance between them a bit to prevent
Z-fighting.
The base model should be left as is, and the glow model should be set to the additive rendermode.
Hopefully this will end up looking alright when the models are lit up:
But it will really look good when the model is in a darker environment:
The effect was improved a little bit here using a light_spot to project an orange glow on the ground in front of the stove.
This technique was also used on the TV in the Christmas tree map:
FullbrightWith lightingIn the case of the TV, the screen of the basemodel was just black, and the images on the TV only existed on the glowmodel. This was done to prevent the images clashing if the player shined the flashlight at the model.
I've only ever done this with static prop models, as I still haven't learned to animate models yet. I'm sure the same technique could be used for animated models, but for something like NPCs or onscreen weapon models I think it would probably need coding to display the two models at once.