Just place it on the same spot and with the same rotation where you have your lamp. The number at the end of the model name is how many degrees it spans out. This currently only supports the "light_fluorescent_farm" models.
Don't like the brightness? Pop into the .vmt and change it yourself! It's as easy as it can get. (spoiler: very easy)
Install by extracting the folder "assets_light_gradient" to tf/custom or by merging it's contents with the tf folder directly. It's your choice how you organize your custom assets.
You can use this anywhere you want, just remember that when uploading a map to the workshop you will have to set me as a contributor. (Even if it's just 1%.) This goes for all content made by anybody, as far as i know.
 "I solve problems. Not problems like 'What is beauty?' because that would fall within the purview of your conundrums of philosophy."