Emergency Lighting | How Long Will That Bulb Last?

How Long Will That Bulb Last?

One of the most important things to consider with emergency lighting is how long the light will last.

There are two issues here. One is the design life of a light bulb itself. The other is how long the batteries energizing the light will last.

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Of course, for those times when the lights do run out, it’s always a great idea to have a backup on hand.

Emergency Lighting: How Long Will It Last?

Electrical light bulbs, fluorescent light tubes, and LEDs can last for thousands of hours. Below is a table comparing the operating lifetimes of various emergency lighting sources showing how long these will last.

If you have electrical power, these lights should last for the hours shown in Table 1.

Emergency Lighting and Battery Power

If you’re using battery-powered flashlights or lanterns, the amount of hours you can get out of fresh batteries becomes important. Here are some interesting facts to consider concerning emergency lighting and battery power.

The capacity of a battery is determined by the hours it can put out electrical current (amps or milliamps)—based on the DC voltage remaining in the battery. As shown in Table 2 batteries are rated in the amp-hours (or milliamp hours) of energy they can produce.

An AAA alkaline battery rated at 1,200 mAH and driving a 120 milliamp load can last 10 hours.

When you turn on your flashlight, it draws electricity (actually milliamps) from the battery. As the battery power is used, a point is reached where the battery does not contain enough DC energy to produce the milliamps of current necessary to drive the light source and the light goes out. How long is this?

Just because a battery contains a lot of amp-hours of stored energy, this does not mean that the battery as a power source will last a long time. It depends on how much current is drawn from the battery to energize a bulb in the flashlight. For continuous light during a power outage, it’s important to know how long a particular battery (or series of batteries) will last if the light is left energized in a darkened room. Researching online provided several data points to help me create Table 3 comparing battery manufacturer battery types and how long their battery products could power a load (e.g. bulb).

How long a battery lasts depends on the load put on the battery—how much stored energy is pulled from the battery. A tiny bulb with the metal electrical conduction path in a flashlight is an example of a load. In a quality flashlight, a D-size battery will last 10 to 15 hours. In a cheap flashlight, it may only last 8 hours. Most D-cell batteries last longer than AA-size batteries. Draw half an amp out of a D-cell and it will discharge in 4 hours. If a 9V battery is rated at 600 milliamp hours (mAH) and draws 25 milliamps (mA) in an energized flashlight, the battery will last approximately 24 hours.  A Duracell rechargeable 9V NiMH battery rated at 170 mAH driving a 17 mA load will discharge the battery in 10 hours. These are all approximations but they give you a rough idea how long your flashlight will keep the bulb energized and lighting the area around you.

According to online forums, batteries can remain charged longer if stored in a refrigerator—not a freezer—a refrigerator

Drawing less from a battery can significantly increase its useful life. Take a look at Table 4. It shows the time that various lanterns will remain energized based on their brightness setting.

As you can see, the longest run times are associated with the use of D-cell batteries. Table 4 can be helpful when selecting the right lantern for you.

While many lighting options exist, the key here is to have a number of brightness and long run time light sources for use when power goes out. No-one needs to be in the dark. Whether it’s a campout, a nice evening on the patio or an emergency power out situation, light is available. Be prepared. Be bright.

(Based on the book Power Out! How to Prepare for and Survive a Grid Collapse)