Overdriving warm and cold white emitters?

Nos · Apr 20, 2009

Hi, overdriving emitters beyond specs is notthing new to anyone.
What makes me wonder is the max. current in the data sheet of the cree emitters.

all cold white XR-E emitters are rated 1000ma max current while warm and neutral white are only 700ma.

Does this have something to do with the red phosphores, and do i have to care about the lower current rating of the warm emitters anyway ? :shrug:

csshih · Apr 20, 2009

hm, I think if you overdrive warm and neutral emitters, the blue light emitted by the die starts overpowering the phosphor, resulting a tint heading towards blue?

LukeA · Apr 20, 2009

The warm white phosphor dissipates more energy at a given power level than a cool white phosphor at the same current.

For example:

Say you have a die that is a Q5 (107 lm min. @350mA) under a cool white phosphor but is a P4 (80.6 lm min. @350mA) under a warm white phosphor. Let's also say that the LED has a Vf of 3.50V at 350mA. The same amount of energy enters each phosphor, but different amounts are dissipated as light. For the sake of comparison, we'll use 242.5lm/W as to convert light output to power. The real number shouldn't be too far from that.

At 350mA, the warm white phosphor dissipates 26.4 lumens' worth of power more than the cool white phosphor, or about 109mW more than the cool white phosphor.

If we say that the bare blue die has a luminous efficacy of 140lm/W, then the cool white phosphor dissipates the difference between the input power to the phosphor (140lm/W*1.225W) and the output power dissipated by the phosphor (107lm / 242.5lm/W), or more concisely, 707mW - 441mW, or 266mW dissipated as heat by the phosphor.

For warm white, the efficacy of the blue die remains the same, but the efficacy of the phosphor decreases. The numbers are 707mW - 332mW, or 375mW dissipated as heat by the phosphor.

The warm white phosphor dissipates as heat 29.0% more power than the cool white. What I'm getting at is that the phosphor of a warm white LED will settle at the same temperature as a cool white LED running at 29% higher power. The phosphor of a warm white LED running at 700mA will have roughly the same temperature as that of a cool white LED running at 1000mA.

So, If you are planning to overdrive a warm white LED, the phosphor will have either approximately 30% less lifetime than a cool white LED at the same current or will have approximately the same lifetime driven at 30% lower power consumption.

Vox Clamatis in Deserto · Apr 20, 2009

hm, I think if you overdrive warm and neutral emitters, the blue light emitted by the die starts overpowering the phosphor, resulting a tint heading towards blue?

Yep, I demoed that a little while ago when I tried to put a SSC P4 emitter in an old model Surefire U2. The first four clicks were well spaced steps in brightness, the last two were brighter but suddenly quite purple. I decided that the legacy electronics weren't suited to regulate the P4 so I reinstalled the Luxeon.

Illum · Apr 20, 2009

Nos said:
all cold white XR-E emitters are rated 1000ma max current while warm and neutral white are only 700ma.

based on primitive observation of die differences the WW has a slightly heavier coat of phosphor leading me to believe that there may be an issue with thermal dissipation in high currents? Yes it is possible that its due to the red phosphors but I dunno... :thinking:

While it is agreeable that the design specifications limit on the absolute maximum allowances I have no idea why you would want to drive it that high...around 1A the efficiency of CREE XR-Es basically goes out the window, your better off using an MC-E:grin2:

I'm just a photographer :ooo: :aaa:
Neutral white

Warm white

Q4

just for kicks, MC-E