Lux to par graph/conversion

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SteakBags

Well-Known Member
What do the experienced LED people think about the accuracy of these graphs? For my specific situation I’m using a 65w 4000k HLG 65.

If I buy a lux meter and multiply my lux by 0.024, am I going to be in the ballpark of an accurate PAR reading?

I included the graphs and video from which they came.
 

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S

Snob

Well-Known Member
SteakBags said:
Looking to avoid the few hundred dollar price tag
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Then Just save up and wait. Lux is not made to measure LED's. There is a reason the PAR meters are expensive. I dont know how nerdy you are, but there are people on the tube that build these themselves.
 
S

SteakBags

Well-Known Member
Snob said:
Then Just save up and wait. Lux is not made to measure LED's. There is a reason the PAR meters are expensive. I dont know how nerdy you are, but there are people on the tube that build these themselves.
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I don’t need it to be exact, and there are conversions for lux to par which is what I’m trying to figure out. I’m growing 2 fairly small plants in my closet, if I can dial in where my light needs to be without spending $500 I’m going to try and go with the cheaper route.

The issue is my LED being too close because I’m limited vertically (36” floor to light) ...if I can get a rough estimate on lux to par I can figure out if and how much I need to dim it down.
 
.Smoke

.Smoke

Well-Known Member
SteakBags said:
I saw this and another calculator online, but they don’t correlate with the graphs which were made using an accurate par meter.
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I think that's the problem of not having a PAR meter for Led.

Yes, we all know an Eye Hortilux HPS bulb is a bit brighter, but the difference in HID bulb variance I'm guessing is a lot less than the variance between a top line Samsung diode compared to a bottom of the barrel one. Making it much harder to get an average to base an equation off of.

Unfortunately, the answer seems to be that your expensive light is gonna need an expensive meter.
Yet another reason that turned me away from Led.
 
Moflow

Moflow

Well-Known Member
If you buy a lux meter just take a reading 18" away from the light and whatever lux reading it says will be the equivalent of 290 umols/m2/s
These Par Maps below will tell you all you need to know for growing.
I would say round 22-24" for seedlings, early vegging plants
20200708_002443.jpg

This Map below is 12" from the sensor
So around 14" for late vegging plants
12" early flowering of plants.
8- 10" away for mid late flowering.
20200708_002908.png
Problem solved.
 
S

SteakBags

Well-Known Member
Moflow said:
If you buy a lux meter just take a reading 18" away from the light and whatever lux reading it says will be the equivalent of 290 umols/m2/s
These Par Maps below will tell you all you need to know for growing.
I would say round 22-24" for seedlings, early vegging plants
View attachment 4617454

This Map below is 12" from the sensor
So around 14" for late vegging plants
12" early flowering of plants.
8- 10" away for mid late flowering.
View attachment 4617455
Problem solved.
Click to expand...
My head hurts from researching this shit literally all day, I completely forgot about using that par map as a reference. Thanks for thinking for me lol
 
S

SteakBags

Well-Known Member
Moflow said:
If you buy a lux meter just take a reading 18" away from the light and whatever lux reading it says will be the equivalent of 290 umols/m2/s
These Par Maps below will tell you all you need to know for growing.
I would say round 22-24" for seedlings, early vegging plants
View attachment 4617454

This Map below is 12" from the sensor
So around 14" for late vegging plants
12" early flowering of plants.
8- 10" away for mid late flowering.
View attachment 4617455
Problem solved.
Click to expand...
so for shits and giggles lets say it read 20,000 lux at 18”, 20,000/290 = 68.96 ....so round up to 69, would that be my conversion number for any lux reading under this light?
 
Renfro

Renfro

Well-Known Member
SteakBags said:
What do the experienced LED people think about the accuracy of these graphs?
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The real question is the accuracy of the meter. Most meters don't accurately quantify only the spectra that the plants use (PAR). Most read two different light sources as apples and oranges making any comparison pointless. An exception to that is a quality PAR meter like the Apogee MQ-500. This meter can read a HPS light or a LED light and make apple to apple numbers out of that.
 
S

SteakBags

Well-Known Member
Renfro said:
The real question is the accuracy of the meter. Most meters don't accurately quantify only the spectra that the plants use (PAR). Most read two different light sources as apples and oranges making any comparison pointless. An exception to that is a quality PAR meter like the Apogee MQ-500. This meter can read a HPS light or a LED light and make apple to apple numbers out of that.
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From what I’ve read it’s only the blurples and that color light that the lux meters won’t read, correct me if I’m wrong but wouldn’t I be fine with my white 4000k spectrum?
 
Renfro

Renfro

Well-Known Member
SteakBags said:
From what I’ve read it’s only the blurples and that color light that the lux meters won’t read, correct me if I’m wrong but wouldn’t I be fine with my white 4000k spectrum?
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They will read HPS differently than MH or CMH, they read all lights differently. They don't measure PAR spectrum, and therefore you can't convert the LUX numbers to PAR numbers. It's just that simple. PAR means photosynthetic active radiation.
 
Renfro

Renfro

Well-Known Member
Unless you are testing lights extensively then you don't need to even have a light meter. Even for checking if a bulb is losing output you don't need a meter, it's predictable but in that case you don't need any PAR numbers, just know what it read new and what it reads now on a given meter. Save the money on a meter to quantify light and use it to purchase something truly useful like a quality pH meter or a better light, you know, something that will actually increase yields.
 
JoeBlow5823

JoeBlow5823

Well-Known Member
I like having mine.... I find when Im reading over 55-60k lux, its to bright. I mostly will be using it to train my plants in my 5x5. Keep them low in the middle hot spot and tall on the outsides.

I also compared my double end 1000w HSP to a friends single end and found my light to be a solid 20-30%
 
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