What factors affect the luminous efficiency of dive lights?

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XTAR

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High luminous efficiency dive lights mean higher efficiency when transforming electricity to light. But do you know what factors affect the lights’ luminous efficiency? Let’s check the factors shown below.

*Light transmittance of lens
When light passes through the glass, some of the light will be absorbed and reflected at the same time. The light transmittance determines how many percent light can pass through the glass.

*Luminous efficiency of the LEDs
The luminous output increases together with the working current. While, more current creates more heat and makes the luminous efficiency decrease with current increasing.

*LED driver efficiency
The driver itself consumes some power when it works. The driver efficiency determines how many percent of the power left and can be used on the LEDs. So higher driver efficiency means less waste of power, and surely affect the luminous efficiency of a dive light.

And someone asked a question about two dive lights’ brightness levels and runtime comparison: under the same 26650 battery, one light low mode 30lm, runtime 32hrs; another light low mode 60lm, while runtime 48hrs. Why does the light have lower lumen but shorter runtime? Actually, there are different types of drivers and what voltages, currents they work with, and also different conversion efficiency of the driver circuit on the lights. The light with 30lm can basically remain unchanged during the burn time, and another light’s output with 60lm actually slowly decrease as the battery voltage drops.

Any thoughts and opinions are also welcome!
 
https://www.shearwater.com/products/perdix-ai/

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