Standard fluorescent lamps and their smaller versions, called compact fluorescent lamps (CFLs), give off light in all directions (360°) and tend to make the room warmer. The battery in emergency lights that use these lamps only lasts a few hours because power is lost when DC is turned into AC. These problems can be fixed by using white LEDs that are very bright. Here is a lamp with white LEDs that can also be changed to work as an emergency light in the bedroom. Its main features are that it works for a long time without stopping, it uses very little power, the light angle can be changed, it has a very long life, and it doesn't give off much heat.

Multipurpose lamp circuit Fig. 1: Cluster LED multipurpose lamp Fig. 1 shows the circuit of a white LED light that can be used in many different ways. The circuit is very simple. It uses a battery charger built around an integrated circuit (IC) called LM317 (IC1) and a few white LEDs. The current going through the battery is limited by the 4.7-ohm, 2W resistor R3. The angles of 60° and 20° are chosen for white LEDs. Three rows of LEDs (A, B, and C) are made on separate sheets of clear acrylic. Twelve LEDs are attached to each sheet, for a total of sixty-four LEDs. The LEDs in the left (A) and right (C) columns are 20°, but the LEDs in the middle (B) column are 60°. All twelve LEDs in each column are connected in series to separate 15-ohm current-equalizing resistors (R8 through R19) as shown in Fig. 2 and to current-limiting resistors R7 (10-ohm, 1W) and R6 (5-ohm, 1W) as shown in Fig. 1. The whole thing is powered by a 6V, 4Ah rechargeable battery that doesn't need to be maintained. In torchlight mode, the light stays on for about 7 hours, and in table lamp mode, it stays on for about 14 hours. This depends on the size and quality of the battery. Only the left and right LED columns are used for the torch mode. These LEDs can shine light as far as 6 meters. In table lamp mode (spread light), only the LEDs in the middle column are turned on. Operating modes

Fig. 2: Arrangement of LEDs for column A, B or C The rotary switch S1 is a single-pole, three-way switch that lets you choose between the table lamp and torch modes. When the pole of switch S1 is in position 1, the C column of 60° LEDs light up and the system works as a table lamp. When the pole of switch S1 is set to position 3, columns A and C light up, and the system works as a flashlight. When the pole of switch S1 is in position 2, neither the table lamp nor the torch modes work. When the power is turned on, LED2 lights up. Flip switch S2 to the "on" position to charge the battery. To see how the battery is doing, flip switch S3 to the "on" position. This will let you know how full the battery is. If LED1 goes out, it means the battery needs to be charged. Figure 3 shows the circuit for an emergency lamp with a brightness control. It is based on Figure 1, but the LEDs are put together in a slightly different way. Built around four multichip (MC) LEDs, it is small and easy to use, and it can work in two ways: as a bedroom lamp or as an emergency light.

Fig. 3: Multipurpose lamp with brightness control In the mode for a bedroom lamp, only one blue LED lights up. This LED is mounted upside down at the top so that the blue light can't be seen straight on. The way the lights are set up gives off a nice, even light. In emergency lamp mode, the 8mm, 80° bright-white, multichip LEDs spread light over an area of 80°, which is enough for indoor use. PCBs for multichip LEDs that are round each have four internal connections. Solder LED17 through

LED20 on the first PCB, LED21 through LED24 on the second PCB, LED25 through LED28 on the third PCB, and LED29 through LED32 on the fourth PCB, leaving 3 to 4 cm between each pair of LEDs. Lastly, put the four circular PCBs and the reflector in a small cabinet so that light can spread around the room. Each LED with more than one chip is as bright as 32 candles. Because of this, if you use four 8mm multichip LEDs, you will get a total of 128 candles. When the rotary switch S5 is turned to the emergency lamp mode, all four multichip LEDs (LED17 through LED32) light up. The DC power source is a 6V, 4Ah battery that can be charged. The charging circuit is based on the well-known IC LM317 (IC2). The battery's current limiter is R21, which is 2.2 ohms and 1 watt. You can change how bright LEDs are (their candle power) to meet your needs. The candle controller is made up of the transistor SL100 (T1) and the parts that go with it (brightness controller). Resistor R24 and diodes N3 and N4 keep the voltage at the transistor's base steady (1N4001). The base of the transistor gets this constant voltage from a potentiometer called VR1 (4.7k lin.). You can change how bright the multichip LEDs are by adjusting the potentiometer. The transistor doesn't need a heat sink.