Why are LED bulbs of the same wattage different in brightness?

January 13, 2023

The reasons for this phenomenon are generally as follows:

① The efficiency of the light source is different

LED lamps consume electricity and emit light. This involves the issue of conversion efficiency. The expression form of light efficiency index is lm/w. This refers to how many lumens of luminous flux each watt of electrical power can be converted into. The light efficiency of LED is only a few tenths of a lumen per watt when it was first born. Now good-quality LED lamp beads can reach 180lm/w, which is thousands of times different. Up to now, the luminous efficiency of LEDs has been continuously refreshed every year. Therefore, it is not surprising that the same specification bulbs assembled with lamp beads of different periods or different manufacturers have different brightness.

② Different power efficiency

LED lamp beads are nonlinear elements with negative temperature coefficient, which are extremely sensitive to changes in temperature and voltage. Therefore, neither the AC nor the DC power supply can directly supply power to the LED, but must be driven by a constant current to work. The efficiency of constant current drivers of different qualities varies greatly, ranging from 50% to 90%. Therefore, even if a light source with high light efficiency is selected, the low efficiency of constant current drive will also lead to insufficient brightness.

③The power label is based on different

At present, the power labeling of the LED lighting market is quite chaotic. Some are based on the actual power consumption of the whole lamp, while others are based on the power of the lamp beads. Since the efficiency of the power supply cannot be 100%, LED bulbs with the same power may be marked with different power by different manufacturers.

④ The area of the light emitting part is different

Two bulbs of different shapes with the same wattage can sometimes look very different in brightness. For example, a small light bulb will appear brighter than a large light bulb. Bulbs look brighter than tubes etc.

This is because the areas of the light emitting parts are different. When the same light energy is distributed on different areas, the luminous intensity per unit area is inversely proportional to the area. Therefore, although the brightness of the light source itself is different due to the different light-emitting areas, the lighting effect is still very close.

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