Measuring Florescent light output

[samarak]

Remember also that the inverse square law applies to point sources radiating equally in all directions. Fluorescent tubes are not an infinite line source (which would fall off linearly) but from the standpoint of a plant a few inches away they're not point sources either, even before you add a reflector. When you add several tubes side by side (approximating a planar source to a plant in the center), it's even more complex at those short distances. I still do theoretical calculations from time to time, but my recommendation if you really want to know what intensity you have in your setup is to buy or borrow a meter and measure it.

Re lumens, I find it a valuable number to have simply because it's one of the few that's almost always available. But as it's a measure of luminous flux (i.e., adjusted for the way human eyes perceive light, rather than how plants do, or of total radiant energy) it's only one of the things I consider.

Steve

[Stray59]

- I had no idea that I would start such a involved thread, but I really am learning a lot! I want to thank all of you for your discussion and input. I am sooooo glad that there are people who are good at and enjoy mathematical problems, because I am horrible with them. I am pretty good with orchids though! I will apply this info to my growing room.
Cant thank you enough!
Steve

[Ray]

Blackvine - wattage has everything to do with intensity.

T5 and T8 HO bulbs put out about 90 lumens per watt. A 4' T5 bulb is 54 watts, so puts out about 4860 initial lumens. Two 2' T5s, together, total 48 watts, so put out 540 fewer lumens than does the single 4' bulb.

However, I agree that Steve's initial question about wattage misses the point. A single 2', 24W T5 will allow you to bloom a high-light plant like a vanda - if you put it right up against the plant, but that's all you'll be able to illuminate. If you want to cover a large area, you'll need more light output so the "density" (good term, Naoki) is sufficient over that entire area, so you'll want more total wattage of bulbs.

[Stray59]

I am going to bow out of the conversation for a while and let you guys debate such things as wattage, density, etc. But I will be monitoring the conversation and will (hopefully) be able integrate your knowledge. Please continue to converse as I am learning more and more!!!

[blackvine]

Naoki - thanks! As with everything in life, I continue to see that the more I learn, the more I realize what I do not know!

[blackvine]

Ray, ditto what I just posted to Naoki. But, it seems we did not answer Steve's question about light. Most newbie orchid hobbyists (like me) don't have a deep interest in the science of light - they just want to insure they are growing their orchids in adequate - if not ideal - light. One of these days, I'll buy a light meter, but until then, I'll use my chart just because it seems to be working with my orchids. Cheers, all!

[The Peloric Orchid]

I strongly recommend buying a lux or footcandle meter. I got one for around twenty bucks on Amazon (just remember that there's around 10 lux per footcandle). That way you can take the guesswork out of light placement. 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.

[Stray59]

Again - WOW !I am amazed that something so widespread in it's use seems to be so complicated to properly implement. You guys keep up the discourse. This is all WAY over my head so I will keep monitoring until it gets really simple - I am a little . And a lux meter sounds like what I need to invest in. Any suggestions to brand or what to look for exactly?
Steve
p.s. - what in the heck is a micro einstein?

[The Peloric Orchid]

Since most meters are for lux measurements, I recommend one that's rated for at least 50,000 lux (which converts to around 4600 footcandles). That way you can make measurements all the from low light to something that's beyond the brightness require of bright light orchids. Unless you're into professional photography, you don't need to spend more than $35 dollars on a light meter.

A micro einstein is basically a measurement of the number of photons. As far as plants are concerned, most photons that fall within visible light are suitable for photosynthesis, so color doesn't matter in terms of a plant being unable to photosynthesize and quantum light meters are calibrated to reflect this.

Even though I have science background, the math and physics behind light went over my head too the first time I tried doing this. When I was trying to figure out what wattage (before I knew about lumens, lux, and footcandles) lights I needed, I realized that there wasn't enough data out there to make an exact calculation, so I bought a brighter light than I guessed that I needed figuring I could always mount it higher.

[Stray59]

The Peloric Orchid:
Thank you for the explanation. I am really non-mathematical; I always focused on psychology and orchids, or for that matter, anything besides math. I had a traumatic experience involving formulaic equations I think - I've all but blocked it from my mind. Needless to say, I am much better with epiphytic roots than square roots. I do have a Rhynchostylis that grew a square root, but I think it was just a fluke !
The answer to my question is a light meter. This is the simplest and most logical solution as I am sure every light bulb configuration, the distance of the bulbs, hood color, etc. makes a difference and a meter will show me what the plants are getting in my (their) home.
Thanks again for the help!
Steve