In a scene where you are filming an actor who is watching television in a darkened or dimly lit room, you can create the flickering effect of the television by pointing a soft blue light at the actor and waving a cloth in front of it as you film the scene. Placing a real television in front of the actor will not usually work, as the strength of the light you use to light the scene will be too strong for the light given off by the television. You need to be careful to test the lighting, as it will look unnatural if the blue light is too strong. Test different strengths of blue filter and view the results on a monitor to decide which combination of light strength and filter gives the most realistic effect.
If you are shooting in daylight and want scenes to appear to be in darkness, you can underexpose the shot by raising the F-stop on your camera lens to a high numeric value. This will make subjects seem darker and fill shadows where the naked eye can see details in daylight. You can then use a blue filter on the lens to give the appearance of nighttime. The blue filter washes away the color that would still be visible and gives a more realistic feel of nighttime, where colors are less visible to the naked eye. Use a white diffused light, meaning the light is dispersed rather than aimed directly at a specific subject, to create a moonlight effect. Place the dispersed white light up high, and have only white light coming from a single direction.
Real fires are not easy to manage from a lighting point of view, as you cannot guarantee the even firelight flicker you need. Firelight flicker seen on a subject needs to be of an even nature or it will be a noticeable distraction from the subject you want your audience to focus on. You can create the effect of firelight flickering on your subject by pointing a bright white light, with an orange filter, away from the subject. This orange light should hit a reflector, made of silver foil-backed card or reflective fabric, so it reflects back onto the subject. Manage the even flickering effect of a fire by shaking the reflector.