Emergency lighting is required by law in facilities such as hotels, office buildings, libraries, hospitals, or apartment complexes. When the power goes out the facility must remain lit along the path of egress. The amount of light needs to average 1fc or 1 lm/ft2 for a during of at least 90 minutes. There are generally 3 ways to power emergency lighting during a power failure: integrated battery backup, inverter, or generator. The rating, load, or capacity of these systems mainly depends on the number of units, distance apart, height placement, and the efficiency of the light source. The light sources used are tungsten, cold cathode, halogen, fluorescent and more recently LED (Light Emitting Diode).
The efficiency of the light sources can be defined as lumens per watt. The lumens per watt ratio describes how much light is generated by the consumption of one watt. It stands to reason that the more efficient your light source is, the lesser the capacity requirements are of your backup power sources. With the advances of White LEDs, LEDs can now be used in 'general' illumination applications. General illumination is also known as ambient lighting; the lighting you need to operate comfortably in a room. Emergency lighting is a type of general illumination. LEDs have a better lifespan and are more efficient than fluorescent, and incandescent light sources. Thus the benefits can be characterized in several ways depending on your situation: smaller batteries, smaller inverter, smaller generator, longer runtimes, less fixtures, longer lifespan or more light.
LEDs are more efficient and allow you to use smaller batteries. SLA (Sealed Lead Acid) or SLC (Sealed Lead Calcium) batteries are the most often used batteries to power emergency lights. They are rechargeable. These batteries look like blocks with two tabs located on the top or side. For the same capacity rating, these batteries are less than expensive than Nickel Cadmium (Ni-Cd) batteries. Nickel Cadmium batteries are smaller, have longer shelf life between recharges, greater recharge cycle count, and have better temperature tolerances. SLA and SLC have typically a useful lifespan of 5-7 years, whereas Ni-Cd is closer to 7-10. Ni-Cd is also more expensive than SLA or SLC due to the price of raw materials. Historically Ni-Cd used when the fixtures are in areas of great temperature fluctuation. Batteries are typically installed onto or integrated into the light fixture and are constantly being charged by the facility's emergency circuit. When the power goes out, the batteries provide the power. The size of the battery when the battery is integrated into the unit affects the size, shape, and weight of the fixture. The weight and size of the fixture affect the price of the fixture because the size of the units and weight determine the required strength, amount, and shape of materials used for the enclosure, and the shipping box.
When the capacity requirements reach a certain level, typically above 50 watts, the batteries become quite large and heavy. They are essentially chunks of dense metal. Heavy batteries are difficult to secure and can place great stress on the enclosure and mountings. Heavy batteries will ship in separate boxes than the fixtures. The reason is due to the potential of heavy batteries shifting during transit which can cause damage to the fixture. The weight of the batteries determine the the minimally allowed 'ECT' or burst rating of the packing boxes. The higher the rating, the more expensive the box. The weight of the battery also affects the strength requirements of the structure of the lighting fixture's enclosure or housing.
Integrated battery lighting fixtures are typically made of thermoplastic and are secured by being connected to an electrical junction box. Thermoplastic enclosures are formed using a process called injection molding. Injection molding is a very fast process that allows you to produce shapes with complex contours in great quantity in a short period of time with low defect rates. The high rate of production and inexpensive material costs make these the most popular designs for integrated battery units. Generally, when the capacity requirement rating of the fixture is under 50 watts, the housing is made of this inexpensive thermoplastic. The battery used is likely 6v 4.5Ah - 6v 12Ah. The battery would weigh about 5 .lbs. Above 50 watts, the fixture's housing is made of fiberglass or steel. Steel and fiberglass are able to support the greater weight demands of larger batteries. Steel and fiberglass enclosures are most basic in shape than thermoplastic ones. This is due to in part to the simpler shapes having less stress points. Therefore, these fixtures are less 'modern' or visually pleasing; typically being classified as industrial fixtures. Unlike thermoplastic, Steel is prone to rust, fiberglass is course and therefore both must be coated, thus increasing price. Lastly, depending on the size, Steel and Fiberglass enclosures are installed using shelves mounted to the wall.
Currently, the most popular emergency lighting fixtures are incandescent (tungsten) using 6v 4.5Ah SLA batteries. The most popular fixtures have 2 heads with a wattage rating of 5.4 watts to 7.2 watts. By switching these fixtures to LED light sources, the smaller, almost by half, lesser capacity, Ni-Cd batteries are able to be used. This allows us to make the units smaller and more light-weight. The reduced materials costs are offset by the increased cost of the batteries and LED's but overall its a win-win. The benefits to the customer are an emergency unit using a better battery with greater cycles and lifespan, a more compact design, longer shelf life, and greater tolerance to temperature fluctuation; a more satisfying product.
See Examples of LED Emergency Lights
located to the right.
Using LED Emergency Lights with Inverters or Generators
As opposed to integrated circuits on fixtures, generators or inverters power entire circuits, or a series of fixtures. These circuits must be dedicated. If there are to be items plugged into the circuits, the plugs must be colored. Generators or Inverters are sized to meet the demands of the items they will power, known as load, and the duration they must power them for. The building code requires that illumination persists for 90 minutes minimum along the path of egress at a level of 1fc average. If the building is already built, great care must be taken to maintain the system and ensure that the load remains with the rated capacity. Over time it may be necessary to add greater load onto the system. Rather than simply opting to increase the capacity of the inverter or generator, it may be more cost effective to review the options of improving the efficiency of fixtures that comprise the current load. There are several ways to do that. The first step is to review the circuit to ensure that no items have been added inadvertently. You should then determine the items on the load, especially the lighting fixtures bulb types. For example, recessed cans may be retro-fitted with CFL, or better yet, LED. In some instances, it may be beneficial to change out the fixtures altogether. For example, if the ceilings are high, CFL does not mimic the direction light patterns of halogen as well as LED does. Also, with LED, you have better control of the beam angles. Beam angle allows you to flood or spot the focus of the light. With greater height you will want a more focused angle.
The efficiencies to be gained are great. For example, if the backup fixtures are halogen bulbs, it may be possible to swap the bulbs over to LEDs which can reduce the load by up to 90%. It is important that before making any permanent changes to ensure that you will be in compliance with the 1fc requirement. You can do this by getting a light meter. The main objective with any life saving device is to ensure that when the time comes, they are able to in fact, save lives by performing to the needed standards. WIth thoughtfulness and planning, it is very possible to improve the safety of the building, while at the same time improving the efficiency. If you are uncertain as to which LED fixtures are applicable to your application, considering contacting the experts at Greentorch Lighting. If you are about to install a new inverter or generator, consider the costs of improved lighting fixtures versus upsized generator. Using LED will give you better maintenance profile, and greater efficiency.
If you are in the process of deciding if an inverter, or generator versus integrated backup fixtures, or for more details, contact The Exit Store.