Use a lamp with very low brightness.

Avoid switching on bright lights if you wake up at night. Even a short exposure can make it harder to get back to sleep. Avoid LED lights in the bedroom and use a night light with a dim and warm light, preferably with a red colour. Also avoid turning on bright lights if you need to go to the toilet during the night. 

Why it helps:
If you only expose yourself to warm, low-intensity light, your cortisol will not increase to the same extent as with bright light. This reduces the risk of disrupting levels of the important sleep hormone melatonin.