As other folks have pointed out, I don’t think you can.
And isn’t that a horrifying concept?
Maximum TL:DR mode engaged here, but as Arlifrex and Ariiah pointed out, to use the Light is to believe absolutely in something, and Lightforged take that, like, fifty steps more in a process that forces the individual to face their inner demons, to literally fight them or die, and is so dangerous you need a partner with you who has already undergone the process (player is already Light Forged during their intro campaign) or someone you trust implicitly who can help you through this process.
And remember, the Naaru are of the Light, they are not the Light themselves, despite how Xe’ra tried to portray herself.
As Kailarra pointed out, the ‘Primal Forces’, Void, Fel, Arcane are all addictive and can influence the mind. Light is no exception and is generally ignored for its addictive qualities because it magnifies positive emotions, and the Light Forging process, again, takes this several steps further, forcing the would-be Lightforged to face their own darkness and burn it away, which is not just a symbolic event, but a mental and spiritual one wherein their fear, their self-doubt, their anger and their despair is all defeated and destroyed, leaving behind only the parts of their being that resonate with the Light.
Now, this shouldn’t imply a Lightforged Draenei, or any other Lightforged being, is without fear, or anger, or any of the ‘darker’ emotions, but they have control over those emotions in a way that those not physically and spiritually fused with the Light can never match. Even the Pandaren Shado-Pan must maintain tight emotional and mental focus to prevent the Sha from effecting them, and that requires decades of training, meditation and experience to accomplish to the level of an individual like, say, Taran Zhu.
There’s also something to be said that the Light is with the Lightforged in every moment of their life. Not just their waking ones, every single beat of their heart is one with the Light. A Lightforged Draenei who loses faith in the Light is losing faith in themselves, and that could be disastrous to both their physical health and mental stability. That said, they can also feel the Light surging through them, as much a part of them as the blood in their veins and the marrow in their bones, and the Light itself is sentient in a way that is difficult to explain, and oft exploited by beings like Xe’ra and her Army of Light, and the Dreadlords who taught the Scarlet Crusade new and horrifying uses of the Light (interesting that now we know why ‘Demons’ like the Dreadlords could use the Light when it was supposed to be inherently hostile to them …), and it worked despite everything because the Light will respond to a strong will, and will enhance and magnify the positive emotions of a potential host.
To love, to hope, to be charitable and kind, all of these facets of the mind are strengthened by the Light, and I imagine doubt in a Lightforged Draenei would be more along the lines of ‘how are we failing the Light’, rather than ‘how can the Light be failing us’, given their countless millennia of indoctrination and sermonizing by Xe’ra, and how it was ‘only’ the Light that saved them from enslavement to the Legion.
Or at least, that’s my TL:DR thoughts.