Nepenthes light readings

[osmosisuk]

Has anyone actually made measurements of the lux or foot candle readings they are growing their plants under, or plants in the wild.
The few mentions I have found led me to illuminate mine at about 10K lux when I recently started using metal halide as a supplementary winter light in my greenhouse.
In some plants this has led to leaf reddening (suprisingly rajah - I thought this liked high light), others e.g. jacquelinae & lowii nothing at all.
I am going to leave them to adjust, its just interesting they seem to perceive this as high light when this is less than 1/10 of summer/tropical sunlight

 

[killerplantsguy]

I just checked the light levels in my greenhouse.  Planst are getting 2500 - 3000 fc.  That is with 60% shadecloth over fiberglass and it's a sunny Winter day.  Had been running lower light levels in the past, but since light has been increased, plants are doing much better.  For example, new pitchers on N. talangensis are nearly 3x larger.

Will be interested to hear others weigh in on this,
KPG

 

[Brian_W]

I have access to a PAR meter, and I'm going to take readings outdoors and compare them to readings from my lights.

It would be interesting to see what the light readings are for Nepenthes in the wild. I don't think that this has been done.

 

[rlhirst]

Just put in a new 400w HPS bulb, and measured it for ya.
1500-2200 fc.

 

[TyFone]

How many Fc is lumens?

 

[tonyc]

Foot-candles and lumens measure different things, the SI unit corresponding to the fc is the lux. Essentially, lumens measure how much light is emitted by a source, fc or lux measure how much light falls on a surface.
Since 1 fc=1 lumen/square foot, and 1 lux=1 lumen/square meter, 0.093 fc = 1 lux, conversely 10.76 lux = 1 fc.
Cheers,
T.

 

[TyFone]

So you cant mesure how much a plant gets in lumens? my growlights has 13400 lumens. How can I mesure the lux then?

 

[Jason Wong]

Ah, I calculated there *should be* about 21222.41 fc

(OMG), then realised it was in lux. Thus 21222.41 lux = ~2000 fc.

That is not taking into account the age of the bulbs, light lost due to inefficient relfectors, etc.

 

[Jason Wong]

Quote[/b] (TyFone @ Dec. 11 2005,9:53)]So you cant mesure how much a plant gets in lumens? my growlights has 13400 lumens. How can I mesure the lux then?

Measure the total surface area in meters the light from your MH is falling on, then divide by the number of lumens to get lux. Divide lux by 10.76 to get fc.

 

[TyFone]

its not MH ;P its flouroscent tubes.

 

[tonyc]

TyFone wrote:

Quote[/b] ]So you cant mesure how much a plant gets in lumens?

No.
How many lumens your lights emit tells us how bright your lights are.
How much of that light is available to be used by your plants depends on a lot of factors, but chiefly how far they are away from it. For a bulb or a single tube the amount of usable light is roughly related to the square of the distance the plant is from it. So, compared to a plant one unit of distance from the light a plant twice as far away receives a quarter of the energy and one three times as far a ninth.
Cheers
Tony.

 

[osmosisuk]

Wow, so you are growing your plants between 2x (rlhirst) and 3x (killerplantsguy) mine. I guess my light levels would possibly be similar in summer, I grow high light orchids and use little shading. I'm really interested now to measure this next year. The reddening I am seing now seems most likely just due to the plants suddenly being shocked by a sudden jump in light in the middle of the miserable British winter.

One slight word of warning - the light your plants get under lights is theoretically the lumens / area the light illuminates. However, reflectors do not evenly spread the light. My reflector (pulsar) has a very uneven light spread, light being relatively low right under the bulb, highest (3x the centre) in two stripes under the trailing edges of the reflector. I don't know if this is typical, or if I have just bought a bad design.
It is also rather difficult to judge what is an illuminated area, as human eyes are very poor at judging absolute light levels. What looks bright to you is not necessarily any good to a plant.

Only way to know for sure - get a light meter or even better (far more expensive) a PAR meter which measures the components of the light the actually matter to plants

 

[lol]

I'm sorry if I seem ignorant, but could someone do this calculation for me? My lights are 45" above the plants, and hit a 30" by 60" area. I estimate lumen output of all lights to be... 14,000 + 4,000 + 4,000 + 8,800= 30,000 lumens without al the sunlight coming through my window. Can anyone calculate the foot candles for me please

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