Testing luxeons at lower current? Does it scale?

Greetings,

I still need to get some kind of power supply (regulated) to test luxeons but a few quick questions:

1. On bare luxeons, without heatsinks, what is a safe amount of current to run through without damage?

2. At lower current, does the results scale to higher currents? Meaning, if a luxeon is brighter than another at 100ma, would it also be brighter at 350ma or 700ma or 1amp? Would Vf also track the same way - lower vf at low current translates to lower Vf at higher current?

Thanks in advance for any opinions.

Moses

[ QUOTE ]
moses said:
Greetings,

I still need to get some kind of power supply (regulated) to test luxeons but a few quick questions:

1. On bare luxeons, without heatsinks, what is a safe amount of current to run through without damage?

2. At lower current, does the results scale to higher currents? Meaning, if a luxeon is brighter than another at 100ma, would it also be brighter at 350ma or 700ma or 1amp? Would Vf also track the same way - lower vf at low current translates to lower Vf at higher current?

Thanks in advance for any opinions.

Moses

[/ QUOTE ]

1. The figure of 100mA is given in a Lumileds document.

2. I have never seen this discussed here but the answer to both questions is "not necessarily". It is *probably* safe to assume that where there is a big difference in Vf or brightness at low currents that it will hold at higher currents but not necessarily in the same ratio.

Here is some raw data

This includes 3 1W whites, and 3 5W (2 white, one RB).

The 3 whites are all the same Vf bin

There are two 5W of the same Vf bin, but the data shows they all 3 should be the same Vf

I'll let the data speak for its self:

<font class="small">Code:</font><hr /><pre>
1W 1W 1W 5W 5WRB 5W
I (mA) Q2J Q2J Q2J V3T S3T VV0U
0.1 2.46 2.47 2.50 4.94 4.98 4.94
30 2.82 2.75 2.81 5.65 5.62 5.67
130 3.05 2.95 3.04 6.04 6.15 6.04
310 3.27 3.14 3.27 6.38 6.57 6.34
620 3.52 3.36 3.50 6.73 6.95 6.64
1060 3.77 3.60 3.79 7.09 7.25 6.92
</pre><hr />

There are several cases where the Vf of a particular luxeon is lower than another at low currents, but then becomes higher at high currents.

THANKS! Re: Testing luxeons at lower current?

Thanks Doug S & evans9162.

Appreciate your response and especially the data. Seems like there is some correlation, although not perfect. But enough it seems to have a general trend once we hit the 130ma and up mark.

Thanks again,
Moses