Question

You have a white light LED with 100 lumens/W luminous efficacy when biased at 100 mA and 1.8 V. Assume the diode has ideal characteristics and that luminous flux is linear with diode current (a reasonable approximation). The 100 mA bias is the preferred current for long lifetime, the diode will catastrophically fail at a current of 200 mA nearly instantaneously (the LED will glow brighter between 100 and 200 mA but not last very long). How many lumens does the diode produce at its preferred bias?

Answer 1

To calculate the lumens produced by the LED at its preferred bias of 100 mA and 1.8 V, we multiply the power consumed (0.18 W) by the luminous efficacy (100 lm/W) to get 18 lumens.

Step-by-step explanation:

The student has an LED that operates with a luminous efficacy of 100 lumens per Watt (100 lm/W) when biased at 100 mA and 1.8 V. To find the total lumens produced at its preferred bias, we need to calculate the power consumed by the LED and then apply the luminous efficacy.

First, we find the power (P) consumed by the LED using the formula P = VI, where V is the voltage and I is the current.

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• P = 1.8 V × 0.100 A = 0.18 W

Next, we apply the luminous efficacy of the LED to find out the luminous flux (Φ).

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• Φ = Luminous Efficacy × Power
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• Φ = 100 lm/W × 0.18 W = 18 lumens

Therefore, the LED produces 18 lumens at its preferred bias of 100 mA.