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What's your Lux


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Guest Maxwell

Not to "throw a spanner in the works"(:-puffin ), but anyone able to measure PAR? Is an app available? By the looks of CMH they would peak higher in PAR than a higher wattage HPS?! Similarly a PAR value of LED vs HPS would be interesting... Thoughts?

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The thing about par is that it's not a widely adopted reading for any bulbs. Some specialised bulbs will state there par rating but unless you import the bulbs directly you won't find them in SA.

 

While we all know lux is light intensity for human vision while plants use par. Now for a home indoor grower measuring par us not easy unless you prepared to fork out big cash. Honestly the home grower also has no need for a par meter , par and lux are very closely linked and if you can measure lux you can get a rough par reading.

 

The reason why I say a par meter is a waste is because like it or not once you have bought all your equipment you are stuck with you par rating and can only increase it by moving lights up and down. Now bring in the phone app light meter , yes it's an app and yes it's probably not very accurate but.... what it does do is give you a reference point . It measures in lux , light intencity , and light intensity is light intensity weather measuring in lux or par.

This is way 90% of the grow community will use a lux  and have things rated in lumen , it's just easier .

 

Here are the multipliers to convert illuminance in Lux to PPFD for some common light sources:

 

Source Multiplier

Sunlight 0.0185

Fluorescent (Grolux) 0.029

Metal Halide 0.0141

Fluorescent (865/840) 0.0135

High Pressure Sodium 0.0122

 

Figures provided by Apogee Instruments.

 

So, we can multiply the Lux value by the multiplier in the above table to find the PPFD in µmol m-2 s-1.

 

 

Worked example:

 

Code:

 

60 cm x 60 cm space (0.36 m²)

250 Watt HPS lamp (33,200 lumens)

 

Lux = (total lumens) / (total area in square metres)

= 33,200 / 0.36

= 92,222

 

PPFD = Lux x factor

= 92,222 x 0.0122

= 1,125

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