I am designing a DIY LED system for my 150 (65 x 24 x24) and I emailed Rick (I didn't email him specifically, just sent a query to ReefLEDlights.com contact us) at ReefLEDlights.com to ask them why they did not sell the Mean WEll ELN 60-48P, but only the Mean Well ELN 60-48D.
His response was
"We actually don't carry PWM drivers due to the spectrum shift they cause in LEDs. We worked too hard in getting the spectrums we carry to have them shift under pwm."
He has a point. This is a true yet not well known fact about LEDs. They change spectrum (wavelength) as a function of both the amperage driving them or the Pulse length driving them. At full current or 100% PWM they act as advertised, but at lower currents or low % PWN they change output frequency.
Here is a link to a short discussion of the subject.
http://www.lrc.rpi.edu/programs/solidstate/cr_effectsofdimming.asp
There is also very significant scientific literature supporting these observations.
The question is whether these effects are worth concerning oneself about.
I argue no. The wavelength at 20% PWM is 456 nm peak and 459 nm peak at 100% peak. For a green LED is changes about 10 nM for peak. Usually the PWN leads to decrease in peak frequency as you lower power. By contrast if yo use modulate current (i.d a ELN-40-48D) to dim the LEDs the frequency increases slightly as you lower power. These are relatively minor changes. So I don' think it is something to worry about
Has anyone else thought carefully or done research on the issue?
I think a discussion is warranted since DIY LED is pretty big these days.
His response was
"We actually don't carry PWM drivers due to the spectrum shift they cause in LEDs. We worked too hard in getting the spectrums we carry to have them shift under pwm."
He has a point. This is a true yet not well known fact about LEDs. They change spectrum (wavelength) as a function of both the amperage driving them or the Pulse length driving them. At full current or 100% PWM they act as advertised, but at lower currents or low % PWN they change output frequency.
Here is a link to a short discussion of the subject.
http://www.lrc.rpi.edu/programs/solidstate/cr_effectsofdimming.asp
There is also very significant scientific literature supporting these observations.
The question is whether these effects are worth concerning oneself about.
I argue no. The wavelength at 20% PWM is 456 nm peak and 459 nm peak at 100% peak. For a green LED is changes about 10 nM for peak. Usually the PWN leads to decrease in peak frequency as you lower power. By contrast if yo use modulate current (i.d a ELN-40-48D) to dim the LEDs the frequency increases slightly as you lower power. These are relatively minor changes. So I don' think it is something to worry about
Has anyone else thought carefully or done research on the issue?
I think a discussion is warranted since DIY LED is pretty big these days.