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Old 04-13-2017, 06:53 PM   #1 (permalink)
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Default Obi's PAR meter results

I've got the PAR meter from Hoppy this week and did the first set of measurements today.

This tank has 4 CFLs and 1 LED growlight arranged left to right in desklamp fixtures.
To do this, I tested with the CFLs that had been there a while and brand-new CFLs just bought. Unfortunately, the old CFLs were 6500K and the new are 5000K (the closest they had in stock).

The numbers I got are in this Google sheet.

I don't quite understand why Test J is less than Test E -- it is likely measurement error, but I did move the sensor around to get max readings. I will have to do another run.

You can see the left-to-right arrangement of lamps in this photo. The sensor is under bulb #2:

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Old 04-14-2017, 06:35 AM   #2 (permalink)
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Default Re: Obi's PAR meter results

I have found that PAR measurements are hard to do accurately. Generally I assume my measurements are only accurate to the nearest 5 PAR. The number after the decimal point is totally irrelevant. CFL bulbs don't seem to produce a constant intensity, but are more likely to produce a slowly fluctuating output. When I turn one on the PAR starts low, slowly builds up to a maximum, then slowly drops back to a more average reading. I have no idea why this happens.
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Old 04-14-2017, 10:29 AM   #3 (permalink)
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Default Re: Obi's PAR meter results

Thanks for posting! So the LED grow light actually works. How does it look compared to the CFLs, especially in color rendition? And what brand is it?

As Hoppy says, PAR meter readings vary a lot. Any tiny change in position of the sensor can have a big effect. I always round to the nearest multiple of 5, or give a range such as 25-30 or 60-70.
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Old 04-15-2017, 07:32 AM   #4 (permalink)
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Default Re: Obi's PAR meter results

Rounding to 5 sounds reasonable.

On the CFLs - yes, there is a warm-up time where the light gets brigther due to either temperature of the gas or maybe the charge between the electrodes. i waited until after that to take the measurements. The fluctuation in intensity after warm-up is a new phenomenon to me.

I thought that there'd be a larger difference between the old and new CFLs, but maybe that's offset by the color temp difference.

The LED grow light is this one from several years ago, no longer made:
https://www.1000bulbs.com/product/11...VGRO38WFL.html

The down side of this bulb is the noticeable chromatic aberration from the offset blue and red LEDs when up close. It would drive photographers crazy without better diffusion.

It looks good from a distance though. The color is warmer than the CFLs, but not purple like many grow lights. I have it on a shorter duty cycle than the others to keep algae growth limited.

It gives a nice accent color to the center, especially when it's the only bulb that's on:
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Old 04-16-2017, 03:54 PM   #5 (permalink)
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Default Re: Obi's PAR meter results

In a standard 10g with 2x of the 17" Marineland Hidden LED Strip Lights I measured 28 PAR. One alone gives 16 PAR. One strip on the front edge, one on the rear.
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