Measuring Florescent light output

[DavidCampen]

Originally Posted by The Peloric Orchid

I strongly recommend buying a lux or footcandle meter. I got one for around twenty bucks on Amazon ... The main downside with these kinds of meters is that they're calibrated to more sensitive in the green/yellow range, much like human eyes, so they won't measure colored light accurately. The alternative is to buy a PAR quantum light meter, but these are much more costly and there's less data about orchid growth in light levels measured in micro einsteins.

The PAR light meters just do not have the green filter that other light meters have. The frequency response of a photocell without a filter is fairly flat so a green filter is added to make the response more closely match that of the human eye.

The inexpensive light meter that I bought on Amazon had a green filter that I easily removed. Of course, that messes up whatever absolute calibration the meter may have had but if you only care about comparing relative values for varied light sources - sunlight, fluorescent, red LED etc. it now matches the PAR meter response.

[Stray59]

Good info to know - I am still in the undecided stage at this time, so I will still just monitor the conversation as see how this develops - I am either somewhat understanding what everyone is saying, or becoming delusional and in that case this really doesn't matter does it? I am leaning toward the meter you are talking about. Any idea of the name of the distributor?

Steve

P.s. I finally found a place to use the chicken emoticon - Yes!

[samarak]

Regarding PAR meters vs. the regular lux/FC meters, I have both, because I'm one of those geeky people. But unless you are, too, I'd go with a lux/FC meter. They are much cheaper, they're perfectly adequate for most people, and virtually all orchid growers and articles about orchids still use foot-candles or lux in the discussion. Few people will know what you're talking about if you mention microeinsteins.

I went to Amazon and just put in "light meter" and got a hit on a 0-200,000 lux (roughly 0-18,500 FC) for $40 US. There's a cheaper one ($25 US) that's 0-50,000 lux (0-4600 FC) but that's a very limited range - it will do for measuring fluorescent lights but once you start measuring you'll want to measure all kinds of light exposures. A sunny day in summer here in NW Arkansas exceeds 12,000 FC, and the unshaded part of my greenhouse can easily be >9000 FC. For the small difference in price, I'd get the better meter.

It's not essential, of course, there are lots of really good growers who have never touched a light meter, but I think you'll have fun with it. And probably learn some things about your setup you wouldn't have otherwise.

Steve

[SueinNC]

Pardon me for butting into this thread but what about the light meters for androids and other phones, has anyone had any experience with those?

[Calbears]

Originally Posted by Ray

Actually, that figure would only hold true if the light output was 20,000 footcandles at 1 foot from the bulbs.

The drop off is an inverse square - twice the distance = 1/4th the intensity, 3x the distance, 1/9th, etc. That means that if the output is 20,000fc at 1" from the bulbs, it will be 5000 at 2", etc.

However, don't disregard the effect of reflectors, as they will redirect the "lost" light from the part of the bulb facing away from the plant, down toward it.

I did some measurements once, using a 2', 24W T5 fixture:

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

[naoki]

Originally Posted by Calbears

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

The unit on the graph is probably correct. Here is my measurement, which matches well with Ray's.

http://www.orchidboard.com/community...tml#post572079

[Calbears]

Originally Posted by naoki

The unit on the graph is probably correct. Here is my measurement, which matches well with Ray's.

http://www.orchidboard.com/community...tml#post572079

Naoki,

For some reason the link is going to the "Orchids in Frog Vivariums" thread but I did see your post and I'm disappointed my 4x4' t5 ho fixture will have to almost touch my plants during this coming winter.

Thanks

[Discus]

Originally Posted by Calbears

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

Lighting reduces its intensity as an inverse square law, hence the (initially "illogically" fast) dropoff.

If you want to try and wrap your head around why, think about a cylinder of paper wrapped around the light at different distances out - the further away your cylinder is, the bigger the surface area gets - at a really quite rapid rate - yet the bulb is still only producing so much light, so it gets "spread" more and more thinly.

This is also why even really bright lights (like flash bulbs) do absolutely nothing in a stadium other than look pretty sparkling on the TV, and give the photographer a disappointing picture of the back of the heads of a few rows in front of them...

[Ray]

Originally Posted by Calbears

Naoki,

For some reason the link is going to the "Orchids in Frog Vivariums" thread but I did see your post and I'm disappointed my 4x4' t5 ho fixture will have to almost touch my plants during this coming winter.

Thanks

That graph was from a single, 2', 24W bulb. Your 4 x 4' fixture, having 4 x 54W bulbs - 9x the light output.

No, you're not going to have to put the lamp that close the the plants.

[Orchidflowerchild]

Originally Posted by Discus

This is also why even really bright lights (like flash bulbs) do absolutely nothing in a stadium other than look pretty sparkling on the TV, and give the photographer a disappointing picture of the back of the heads of a few rows in front of them...

And also why sitting plants "near a window" is not really likely to garner much success unless they are pretty well IN the window. Also why an office desk is a horrible place for a plant. Light is important to consider, but yo0u also have to consider direction of light, duration of light, intensity of light, and angle of light. I bloom Cattleyas under t-8 (anmd back in the day even T-12s!) but I do keep the leaves within 4" of the bulbs.

The human eye is pretty good at making dim lighting look brighter to our mind than it is.

-Ceci