In a darkroom, safelights are used to give off the maximum amount of light possible without harming the sensitive materials being processed. They give off light that won't expose or fog the photo paper. Most safelights use a filter and an incandescent lamp to do this. A sodium vapor light only emits wavelengths that won't affect photo paper, enabling you to have more light in the darkroom without fogging the paper. Safelights can still fog paper if they are too close or too bright.
You can also buy sleeves that fit over fluorescent tubes, turning them into safelights. Be careful with fluorescent lamps because they are filled with gas. When the gas is excited by electricity it glows and when the electricity stops the gas stops glowing. However, it can take up to two minutes for a fluorescent lamp to stop glowing, so make sure they are dark before working with sensitive materials. You will need to make sure your safe light is actually safe enough for your darkroom. They work the best when the light is indirect or reflected. Never point it directly at the sensitive materials. Safelights are for working in the darkroom while processing your film, but when you are doing other tasks you can and should use regular lighting.
Safe lights can range in price from about $10 to a few hundred.