I have a bunch of these PAR lights below. They work with DMX and have per LED PAR 3 red, 3 green, 3 blue and 3 white LEDs.

I can set the value for the red, green, blue and white lights independently (so four values, where 0 = off, 255 = max intensity).

When fading I had the idea to let the values from all colors go up from 0 to 255 and back. However, there are some issues:

  • Some colors do not turn on unless having a minimum value (e.g. red at 8, blue at 2 etc).
  • Some colors do not seem to have the same intensity curve as others (meaning value 10 for red has the same intensity as 2 for green)
  • Some curves are far from linear (meaning the intensity brightness from 2 to 10, is much bigger than 100 to 200).

So I have the idea to 'measure' the values per intensity and make my own intensity curves.

But I wonder what is the best way to do this? Probably by using a LDR but maybe there are better ways?

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  • \$\begingroup\$ @RandyNuss I'm into microcontrollers, but I cannot use PWM since the devices with with DMX, not with PWM. \$\endgroup\$ Apr 22, 2019 at 18:35
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    \$\begingroup\$ Most LED 'PAR' lanterns have a mode that can be configured to give you a dimmer channel as well as the individual colour channels, this is generally vastly better behaved then trying to get a smooth fade without colour shift on the RGB controls only. \$\endgroup\$
    – Dan Mills
    Apr 23, 2019 at 23:27
  • \$\begingroup\$ @DanMills I checked today, but I'm afraid it doesn't make a difference (I have a 'Master Intensity' channel and separate Red, Green, Blue and White channel, but I tried several combinations without any difference. Guess that's why these were just around 10 euro ;-) \$\endgroup\$ Apr 24, 2019 at 21:54

1 Answer 1


Assuming you have the control side of things sorted to adequately vary the lights across their full spectrum I would suggest a proper light intensity sensor such as the BH1750. Sensors such as this are only a few dollars, have digital interfaces and can measure the true lux from 0 to 65535. LDRs might get you a ballpark figure but require proper calibration to obtain light intensity readings.

Bare in mind that the intensity of particular wavelengths of light as perceived by the human eye will differ to that of measured intensities so the eventual curve you decide to use to control these LEDs will depend on the effect you're after.

  • \$\begingroup\$ Thanks for this answer; I will order one and check if it works.. meanwhile I can do other functionality and check the human perception. \$\endgroup\$ Apr 22, 2019 at 18:34

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