Overall conversion efficiency of phosphor in white LED

Anatoly V. Feopentov, October 2006

Links

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Lumileds
Phosphor Global Summit 2006
Intertech

Introduction

This is a method of calculation of phosphor overall conversion efficiency. It is used as a part of calculation of pcLED general efficiency. But it is also good for estimating the quality of phosphor itself.

Advantages and disadvantages

What are the advantages of such way?

• The conversion efficiency is calculated quantitatively without using empiric factors
• This calculation describes reflection losses on the surface of phosphor
• The calculation is performed in energy variable (frequency) which is more correct than wavelength

What are the disadvantages of ordinary technique ^1,2?

• The calculation does not include reflection losses
• The calculation is based on wavelength

The situation is that in common case the centroid wavelength of some spectrum is not equal to velocity of light c divided by centroid frequency of the same spectrum

But the frequency is better for using as energy variable because the centroid frequency matches to average energy. Therefore, it is more correct to calculate the efficiency as a function of frequency.

Formulas

So, the overall efficiency is described as

where

In this equation first part describes reflection losses on phosphor.

Second part represents scattering losses in phosphor.

Third part shows energy loss due to stokes shift.

To simplify the estimation of phosphor overall conversion efficiency the equation can be rewrited as

where

Summary

1. There is one coefficient for estimating the conversion of radiant energy by LED phosphor.

2. It includes all necessary fundamental characteristics.

3. It was found more convenient to use one coefficient instead of a number of heterogeneous factors.

References

¹ R. Mueller-Mach, G.O. Mueller, M.R. Krames, T. Trottier, “High-power phosphor-converted light-emitting diodes based on III-nitrides”, IEEE J. Selected Topics Quantum Electron., vol.8, pp.339–345, Mar.-Apr., 2002.
² G.O. Mueller, R. Mueller-Mach, “Color conversion of LED light”, in Proc. of Phosphor Global Summit'06, March 13–15, San Diego, CA, 2006, p.15.