Studies have shown that even the tiniest bit of light can help people survive psychologically underground. However often people do not consider the short life of light sources and end up in complete blackness. That is why you need to make sure that you are including everything that you need to keep the shelter lit. This is especially true if you are locking yourself in against a threat like fires or a nuclear fallout.
During most disasters electric lights completely fail. This leaves you to use your imagination to create an adequate light source. Flashlights should not be used continuously for many hours. Not only do the batteries fail but the lights can fail too.
One efficient lighting rig-up could be created with a large dry cell battery or car battery and a low-amperage light bulb. This will give you a low-watt light for about ten to fifteen nights. Just remember to always use a bulb of the same voltage as the battery and to use a small high resistance wire such as a bell wire with it.
If you prepare in advance you can also connect small twelve volt bulbs to a wire and then connect it to a car batteries.
You should also stock your shelter with candles and take all the candles you can with you into a shelter. Make sure your matches are kept in an airtight waterproof container such as a Mason jar. Humidity in shelters can cause matches to become so damp that they cannot be lit.
You can also make safe expedient lamps for shelters. These are long lasting shelter lamps that are made of cooking oil or fat and a small lamp wick that is placed inside the jar. This type of lamp is very practical as it burns only one once of oil every eight hours. Another bonus to using this type of lamp is that it also traps mosquitoes and bugs that are attracted to the light and then fall into the oil.
Remember as well that the effect of any light can be magnified with a mirror, aluminum foil or white boards. These materials reflect light and make the place seem better lit.
Remember too that it is can be disastrous to light a fire inside a shelter as the smoke can cause a build up of carbon monoxide. Gasoline and kerosene lamps should also not be taken inside a shelter because they also off-gas. If gasoline or kerosene lamps or knocked over the results can be tragic for the occupants.