Re: Anyone experimenting with LEDs?

[busko at stsci_edu (Ivo Busko)]

The Eng Family <engfam at axion_net> wrote:

>Hi Ivo,
>
>Are LEDs 'equal' in spectrum across the board or are they peaked in certain
>areas?  I know most of the 'white' LEDs claim to be ~5000-8000K range
>(checkout the Luxeon Star with a range of ~9000-12000 and it's more
>powerful ~65000 mcd vs ~3000-5000 mcd of normal white LEDs but then it uses
>200mA vs 20mA).

From what I saw so far, spectral characteristisc of white LEDs vary 
widely from manufacturer to manufacturer. In general these LEDs have a
broader emission responsible for the "white" we see, and a strong
peak at the blue end of the spectrum, that we don't see well but other
detectors such as digital cameras (and plants ? and algae ?) may see
very well. There seems to be large variations in the spectral characteristics
of the broad emission, caused likely by the phosphor properties used in
each case.  It seems to me the whole issue of CCT (correlaetd color 
temperature) is still unsettled among manufacturers. There seems to be
a wide variance in perceived color temp in between different batches
of the same manufacturerer, and even within the light beam emited by a
single LED. Because of these still large intrinsic variances, white LEDs
are being recommended now for use only in applications where color 
perception and redering are not an issue. In short, they seem to be
pretty darn difficult to manufacture within any consistent set of
specs...

- Ivo Busko
  Baltimore, MD

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