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Talking Photometry

Our technical blog helps you keep up to date with developments in LEDs, solid state lighting and the world of photometric measurements. Our blog is updated regularly with news and useful explanations. We also publish "Talking Photometry", as an email bulletin delivered direct to your in-box. Click here to email us and register to receive our regular e-bulletin.

Picture   LED Colour Zoning   Computer
Directory   Colour Zoning from LEDs
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#16 What is "Flicker" and
    why is a problem with SSL?

#15 Measuring colour
    uniformity of LED arrays

#14 LED colour zoning

#13 Colour difference

#12 Photobiological safety -
    don't get burnt

#11 Are halogens history?

#10 Understanding
    photometric data files

#9 Origins of the metric

#8 Scotopic photometry

#7 The torch with the
    power of a million candles

#6 Claimed vs. actual CCT

#5 Useful lumens and
    Energy Efficiency Index

#4 LED specifications - fact
    or fiction?

#3 Is the perfect
    integrating sphere perfectly

#2 Guide to colour

#1 Guide to CCT

  The picture above illustrates the problem of colour zoning from LED spotlights. This is a true colour image (no Photoshop shenanigans!) in which there is a high colour temperature (blue white) central zone surrounded by an area of low colour temperature (yellow white). The problem occurs when the blue light from the LED passes through the phosphor coating. In the forwards direction, a minimum of blue light is converted to longer wavelength light by the phosphor, hence the light in that direction appears more blue (high CCT). However, blue light passing though the phosphor at higher angles is more absorbed due to the longer optical path length and hence more blue light is converted to longer wavelengths. Consequently, light at higher angles appears more yellow (low CCT).

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  Talking Photometry is published as a quarterly email newsletter to registered contacts of Photometric Testing. To receive our email bulletin direct to your in-box, click here to register.


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