Flashlight bulbs can be divided into several types according to the different luminous principles of the emitter. The most commonly used are incandescent bulbs, high pressure gas discharge lamps (HID) and light-emitting diodes (LED). They all have their own strengths and weaknesses.

Incandescent bulbs have a short life span, emit less light efficiently, and are much less bright than LEDs for the same amount of power, or vice versa. But the advantages of incandescent lamp is LED can not be compared, incandescent lamp spectrum continuous, so that the color rendering is very good, color distortion strong identification. And incandescent bulb price is very cheap, easy to supplement, and incandescent lamp does not need to drive circuit, can direct drive, simple structure, easy maintenance. Incandescent bulbs are usually filled with inert gas to increase their life. The most commonly used are nitrogen, argon, krypton, xenon, hence the names argon, krypton, xenon, etc. Some incandescent bulbs are filled with halogen material in addition to inert gas, hence the halogen lamp. For example, iodine tungsten lamp, bromine tungsten lamp belong to halogen lamp.

Krypton gas cylinders

LED is an emerging technology that has developed rapidly in the past two years. Because of its long life, high light efficiency and energy saving, LED is becoming more and more popular. Its disadvantage is that the spectrum is not complete, color rendering is not good, the price is expensive, and relatively delicate, need to drive through the constant current circuit. Now the most widely used flashlight in the United States is the CREE company's high-power LED series. Its LED is divided according to the light efficiency grade, now the mainstream has Q5, R2, R3, R5 these several grades. At a current of about 3W at 1A, Q5 can reach a luminous flux of 250 lumens while R5 exceeds 300 lumens. LED has a great advantage in light efficiency under low power, but with the increase of power, light efficiency will decrease, and too much power will cause serious heat dissipation, reducing the life of LED. According to the current state of technology, the single core LED 3W is basically the limit.

High-voltage gas discharge (HID) technology is another kind of light-emitting technology, the principle is through the arc light, there is no filament like incandescent lamp inside. HID lamps are filled with a variety of gases, most of which are xenon, so they are sometimes called xenon lamps, but be careful not to be confused with xenon lamps in incandescent bulbs. The xenon lamps used in many car headlights are called HID lamps. The advantage of HID is high light efficiency, close to LED,35W HID can reach 3000LM light flux. Glows have a higher color temperature than incandescent bulbs, are close to sunlight, and, in contrast to LEDs, are more advantageous at high power. The disadvantage of HID is that it needs rectifier to start, and it needs large current of the moment when starting, so it has high requirements for lamp design and power supply. And HID is not suitable for the production of low-power flashlight, now basically the lowest power of HID flashlight is about 9W.