Measuring Flicker in lights?

[overclockwise]

Hi BRS,

I've been shopping around for new LED fixtures and the YouTube videos on the performance of individual fixtures put out by the BRS team has been invaluable. However, I have a sensitivity to LED flickering and it has been difficult in obtaining flicker values for aquarium LED fixtures.

In addition to measuring a light's performance regarding health and coloration of corals and fish, I believe that LED flicker should also be measured in order to for the health of the viewers and owners of the fixtures.

Is this something that could be incorporated in testing lights in the future? Instruments already exist for this purpose (ex: UPRtek MF250N) but it's beyond the reach hobbyists' budget.

Thanks,
G

References:
http://www.bio-licht.org/02_resources/info_ieee_2015_standards-1789.pdf
https://www.energy.gov/sites/prod/files/2015/05/f22/miller+lehman_flicker_lightfair2015.pdf

 

[HolisticBear]

I believe the flickering is heavily dependent to the % power output. Running your lights at 30% output produces a great deal of flicker compared to running at 100%.

I was able to take pictures at 1/50s when my lights were at 30% (a black band in the picture). Fine at 1/200s. But at 90% power, no black bands at 1/50s.

Does this mean we can reduce flickering by not buying overpowered fixures and running them at a fraction of their output?

 

[overclockwise]

I believe the flickering is heavily dependent to the % power output. Running your lights at 30% output produces a great deal of flicker compared to running at 100%.

I was able to take pictures at 1/50s when my lights were at 30% (a black band in the picture). Fine at 1/200s. But at 90% power, no black bands at 1/50s.

Does this mean we can reduce flickering by not buying overpowered fixures and running them at a fraction of their output?

Most LEDs are dimmed via PWM on the driver. The light output is proportional to the PWM's driver's duty cycle (how much time the LED is lit up per cycle represented in %). For very low percentages, the LED is going to be off for a longer time per cycle so the flicker becomes more noticeable. Inversely, the higher the duty cycle, the less flicker is seen with 100% having zero flicker (LED is on 100% of the time).

See page 6 of this: https://www.energy.gov/sites/prod/files/2015/05/f22/miller+lehman_flicker_lightfair2015.pdf -- notice how on lower percentages, the gap when the LED is off is larger.

So the short answer to your question is yes but most fixtures are made to fit various tanks. My current solution is really to adjust the amount of light reaching the tank through height adjustment. For example, I drive my LED blackboxes at 100% so there's no flicker but I have my lights at about 20" above the water level so I get the correct PAR levels and not cook corals.

Tip: To catch flicker at higher %s, try running setting your shutter to a higher speed. try 1/300s or 1/500s.