Originally Posted by Ellen H (Post 883867)

Super bright and cool are what I'm looking for...whatever works best for the plant's growth and flowering.

My SO is a Physics professor...I love him and his enthusiasm for the subject but I glaze over after just a couple of minutes of his "explaining" :rofl:

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Ok. So it has a big spike of blue which I understand is more for vegetative growth, right? I'd also need a bulb with more red spectrum for flowering?

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Sorry folks, I'm really messing up the "reply" to specific posters. Sorry for any confusion.

Originally Posted by wisdomseeker (Post 883865)

By no means am I trying to start a pissing contest, but I'm a bit confused with your post. 6500K refers to kelvin temperature (sometimes referred to as CCT or correlated color temperature), not spectrum. Science jargon aside: kelvin is loosely used in lighting as an overall measurement for the color temperature of light (sort of like an indicator of the perceived color of a light source). The higher the temperature (K), the bluer the light will appear. The lower the temperature, the warmer the light will appear (more red). Color temperature (K) has little to do with spectrum. You can calculate kelvin (K) from spectrum, but you cannot know spectrum based on kelvin.

A kelvin number (6500k as an example) means there is a strong emission line at that frequency. Kelvin temperature consists of almost an infinite number of wavelengths to produce a perceived color. Different spectral emission patterns (nanometer wavelengths) can produce light of similar color (example: 6500K).



A really good point. I like to use light that is beneficial for my plants, but also want light that appeals to "my eye". Unfortunately, some of the LED 'grow lights' consist heavily of blue/red light. Maybe okay (or maybe better than okay for plants) but sure the 'heck' does not look good to my "eye". I personally like to look at my plants under a white light (with a touch of warmth). Many of the LED 'grow lights' with good spectrum and a high CRI (color rendering index) will produce a nice white-colored light in appearance, and it really does justice to both the leaves & flowers of the plant ~ within the 'eye' of the beholder.



The tried and true mix of 3500k & 6500K has worked for many people for a long time. Opinions will vary (vastly) in regards to your questions about "full spectrum", specific kelvin temperatures, and what's "best" for growing orchids.

Originally Posted by Nexogen (Post 883880)

That's the idea! It's a joke...

Originally Posted by Ray (Post 883871)

Anecdotally, plain old warm white seems to be adequate.

So do you think the office/warehouse type of T5 LED's would work to grow plants? They are vastly cheaper than bulbs marketed as "grow lights". But most of them, although they may say "full spectrum" on the spec sheet don't mention PAR values.

Grow light bulbs that put out 50-60 lumens/watt are grossly inefficient; even some of the cheapest white lamps put out in excess of 100-120.

Finding retrofit lamps to replace the T5's might be aesthetically best, but might be pretty costly. As I'll be moving to lights over this winter, I'll likely invest in several of the Cree floodlights available from Home Depot.

Originally Posted by wisdomseeker (Post 883843)

A couple of questions.

What brand of T5HO fluorescent fixtures are you presently using (4ft bulbs? reflectors? type of ballast)?
Brand/cost of tubes you are using now?
Is plant growth and flowering favorable using your existing fixtures/bulbs?

The reason I ask about the type of ballasts used is because most "direct drop-in" LED replacement tubes (aka: "plug & play" or "ballast compatible") usually only work with electronic/instant start/programmed start ballasts.

Lighting can definitely be an extremely complex subject ~ and can definitely be difficult to explain and support. It can also become confusing when technical terms are thrown into the mix (watts, lumens. lux, foot-candles, PAR, PPF, PPD, *efficacy*). Just an opinion for what it's worth... I believe a better way to evaluate light, when applied to plants, is to know the type of light needed to support photosynthesis in plant life (especially understanding the parts of the light spectrum most useful for plants).

So on that note... most good quality light manufacturers provide data and graphs for their products: PAR (photosynthetic active radiation - basically light needed to encourage photosynthesis), PPF (photosynthetic photon flux - basically a measurement of the total amount of PAR that is produced by a lighting system each second), spectrum analysis, and *efficacy*. The "Active Grow" LED tube you mentioned does just that, and the specs look pretty good
https://activegrowled.com/wp-content...Data-Sheet.pdf

Why is *efficacy* useful? Calculating efficacy of a light source will give you an idea of the amount of electricity used compared to the light produced. The higher the efficacy, the more money you will save on your electrical bill. Efficacy = luminous flux/power (Lm/W). The "Active Grow" 4ft. tube is 24W. A typical 4ft. T5HO fluorescent tube is around 54W with an efficacy of around 100 lumens per watt (Lm/W). As to spectral data for a T5HO fluorescent tube, I really like the "Hortilux" PowerVEG PowerVEG FS+UV | EYE Hortilux

Something to seriously ponder if you decide to go with the direct drop-in LED tubes (especially when trying to cut costs with buying 12 tubes)... a mix of these: 5000k T5 LED Tube - 25.5W - 5000K - TCP L25T5D5050K and 3500K T5 LED Tube - 25.5W - 3500K - LifeBulb LBT5F3335B could work for your purposes. As good as the others you mentioned? Maybe, maybe not > might be worth a try.

Originally Posted by Ellen H (Post 883897)

So I had a look at these...if my math is correct, the efficacy of the 5000K ones is about 138. Seems good right? I just have no idea from the spec sheet how to gauge whether or not it will provide usable light for the plants.

The Hortilux looks pretty cool. They are the only one I've seen that mention the importance of UV light for the plants and I guess their bulbs supply both UVA and UVB. Is there a real benefit of UV light for the plants?

Originally Posted by Ray (Post 883910)

The color temperature of white LEDs and fluorescent lamps is of little concern, as it is a correlated or corrected color temperature. In other words, it is correlated to look like that color temperature to the human eye, which has very little to do with what the plants get. Both types of lamps use blue or UV light to excite a phosphor that emits light in a series of peaks, not a continuous spectrum.

The bottom line is get the most wattage you can; the other parameters are secondary.

When comparing lamps of equal wattage, I recommend getting the one that is most efficient, i.e., lumens output, and in a tie with that, the one with the higher color rendition index (CRI).

As to "how many do I need", I don't think anyone can answer that directly, as it depends upon the size of the area, it's shape, the types of plants to be illuminated, the spread of the lamp, and the distance from the lamps to the plants. I am usually one to overdo everything, but for my 1' x 4' benches, I'll likely start with three of the 18 watt Cree floodlights, suspended about 24" above the phalaenopsis plants. If I see they are getting too dark, I'll simply lower them - in small increments, so I don't burn them.

Originally Posted by dshallpost (Post 894497)

One thing that surprised me is that these lights put out a fair amount of heat.