Generally speaking, LED lighting source can emit single direction lights. Super-narrow beam angle design typically used in flashlight applications should not be taken into account. Here we just think about general LED lighting applications. In fact, LED lighting sources used in general LED applications cannot send out 100% single direction lights. There are more or less some lights will be emitted into other sides. After packaging, LED chips even emit light from back. This has nothing to do with the workmanship, materials or quality of LED chips. In widely used LED applications, engineers need to invent projectors with high light-reflecting rate to help reflecting this backward emitting light. No matter what type of material people used to produce projectors or other light reflecting covers, it is inevitable for optical energy to be wasted. But LED light consumption is indeed reduced.

 

 

We are going the make a small comparison in intensity of illumination between traditional energy-saving lights and LED lights. Feature above shows the different luminous flux between traditional energy-saving lamps and LED lamps (blue line represents the luminous flux curve for energy-saving lamps and red line represents the luminous flux curve for LED lamps). From this picture we can see that the luminous flux of energy-saving lights within 1 meter is approximately 584lm, while that of LED lamps is around 595lm. The luminous flux of these tow lights are similar (The advantage of LED lights is insignificant). All of them are installed by projectors with same reflecting factor. However, when senses held in a distance longer than one meter, LED lamps perform worse than traditional energy-saving lamps. It is obvious that traditional lights can be replaced by LED lights that only consume half power.

 

LED light consumption only half as much as that of traditional light is incorrect. Not only in LED down lights, but also in other LED lighting applications, like LED tubes, LED bulbs, LED high bay lights, LED street lights, this theory cannot be proved. However, without thinking of the reflecting effect of projectors, LED lights consume much less power than traditional lights to have same luminous flux. But the total light consumption is still more than half of traditional lights.

In recent years, many people raise doubts about the energy saving function of LED lights. Does LED light consumption really half as much as that of traditional light? Theoretically, this can be realized: traditional light source is full-angled (half of which is useless light), while source for LED light is half-angled (none of which is useless light). However, this theory is too subjective to be used. Obviously, people who presented this theory had little acknowledge of LED applications and LED lamps.

 

 

Under what circumstances traditional light sources are considered as half efficient?

1. There is no other lamp tool, like projector, during the installation. The light on the opposite side is directly emits to sky.
2. The back of the light source is a rather high ceiling with very weak light reflection capability.
3. The internal side of the lamp is completely black, all the light emits from the back will be absorbed totally.

 

However, in practical lighting applications, reflection lamp tools (projectors) are necessary for different purposes. In order to fully use the light, the internal of projectors will be mounted by all kinds of instruments with light reflection functions: lens reflection or diffuse reflection. Even for those filament lamps used in a very early age (with no reflection lamp outer covers or projectors), the reflection rate is as much as 70%. Most of the light would be reflected though ceilings and walls, if they had smooth surfaces. Nowadays, fluorescent lamps are widely used all over the world. This type of lights has no specialized projector, still using walls reflecting.

 

Even traditional lights have no effective projectors like LED lights does, they still can reflect most of the light emitting by light sources. However, LED lights which have been designed applying projectors with pretty high reflecting factor cannot 100% reflect the light coming out from light sources. However, it is cursory to judge that LED light consumption only half as much as that of traditional light is incorrect. It is not a problem as simple as “whether the earth is round or square?” Reflection ability is part of the optical-energy-converting efficiency of LED lights. There are many other aspects need to be considered. For example, LED street light itself has very high converting rate from electricity energy to optical energy, which contributes most of its much lower LED light consumption.