Also some of my sungold tomato plants that sprouted 3-4 days ago are looking sad and yellow, not terrible but definitely not great. I used mew miracle grow potting soil and leek and peppers in the same soil are doing great. I have rotated them under a different grow light with no change.

Is there any point in turning the the "bloom" switch on my grow lights? Maybe that is it? Do tomatoes need "different" light compared to other plants?

Those lights should work fine until you can start hardening off the plants. How close are the lights to the plants? They should be 3-4 inches away.

tj

Light is light. Those bulbs provide plenty. I never pay extra for "grow lights". Waste of money. They'll get more light than they will outside, when they'd endure cloudy days. So tuning the spectrum with grow lights just tries to duplicate conditions you'd never have outside anyway. But be sure seedlings are an inch or two below the bulbs, and lower them as they grow to keep their tops near the bulbs. So you have a growing area that's maybe 48x6".

If this setup isn't inside the house, I should add that fluorescent lights produce enough heat that it's pretty easy to keep things warm by throwing a blanket over the whole thing. Adjust the throw to regulate the temperature. Somewhat harder with LEDs, because those produce little heat.

If your tomato sprouts aren't doing well, I'll wager it isn't because of the color of your lights.

They are excellent! Nothing scientific to back me up, but in my experience, seed germination under a mix of warm and cool spectrum fluoro tubes is comparable to LEDs, seedling growth is not -- the seedlings did better under the fluoros than they do with the LEDs. Faster growth and stockier growth, mainly.

Problem is, I got a fancy-schmancy light cart set up that came with LED fixtures, so I can't go back to using the fluoro tubes; I would if I could.

It might be the mix of warm and cool spectrum light or the fact the fluoro fixtures emit more heat, or both. IDK. I just know my stuff did better when I had fluoro bulbs.

Very interesting. I thought it was better with LED grow lights BUT I never really compared it, maybe I just "assumed" it.

One nice thing about the 4' long light is I have it hanging by the center, I can add a little weight to make it slope, higher plants on 1 side and lower plants on the other.

Typically the last 2-3 weeks I leave them outside (after hardening) in a cold frame with heating matt if needed. I think really gets them growing.

I should clarify -- I don't have the specialty grow lights, just the regular LED tubes.

This is a little confusing. The optimum suitability for plants isn't about fluorescent or LED. It's more about the color of the light. "Daylight" (5000-6000K, bright white) is somewhat more appropriate for plants than "Soft white" (2700-3000K, muted white, sometimes called "warm white"). "Daylight" has more blue. You can get either color with both LEDs and fluorescents. As I said, either color should work OK, for bulbs with similar luminous output, assuming the seedlings get enough of the light. For general indoor lighting, many people dislike "Daylight", though, so it may be a little harder to find. But the difference between LEDs and fluorescents is wholly the electrical power per lumen and how much heat they put out. The color of grow-lights might be slightly more optimal for long-term plant growth, but considering how little they are used for seedlings, where plants are eventually planted outside, they can't make much of a difference, except in the thickness of your wallet.

Not well appreciated but a cloudy sky has a higher color temperature - more like 8000-10000K. So it is bluer than daylight, but of course under a cloudy sky plants get a lot less light. Of course, when the sky is clear, but your plants aren't getting hit by direct sunlight, the blue sky has a color temperature of 15,000K or so. The rising and setting sunlight has a much cooler temperature. So grow-lights try to reproduce the illumination that plants outside really don't get that much.

I don't know what the K of the LED tubes I have are, they came with the cart, it was probably noted in the catalogue but I never paid any attention. I'd look at the printing on the end of the bulbs, but the light cart is in use and I don't want to fiddle with re-adjusting things to get the bulb out to look (my eyes aren't sharp enough to see from a distance). If I had to guess, I'd guess 4000-5000K.

Like I said, when I used fluoro tubes, I used a mix of warm and cool -- I don't remember if they were labelled by color ("cool" vs "warm") or by K, it was so long ago and things off the shelf were labelled differently back then, but anyone who wasn't color blind could see the difference -- the warm bulbs looked kinda peachy, the cool bulbs looked blue-ish. This was long before the days of LED bulbs, and an old trusty seed-starting book (that I still have!) recommended this type of set-up.

IDK enough about lighting technology to comment definitively whether the plain ol' LEDs are full-spectrum bulbs, or even if my old fluoro tube set-up created a full-spectrum situation. Sunlight is full-spectrum, but just because a bulb is labelled as "daylight" doesn't necessarily mean it's full-spectrum -- the term "daylight" refers to the color temperature of the bulb (light output as we see it -- cool color vs warm color). I want to say "daylight" bulbs lean heavily into the blue spectrum but not enough red, but again I'm no expert on this.

Like I mentioned, IDK exactly why my seedlings did better with the fluoros, whether it was something about the light itself or heat emission, or both. I also have more surface mold problems with the LEDs, which might make sense looking at it from the heat angle. Oh well, whatever the factor, my stuff did better with the fluoro tubes, but that set-up is long gone.

"Cool" is usually "Daylight", and "warm" is usually "Soft white". But again, you grow seedlings under lights for just a couple of weeks. After that, they're out on their own. You'd like your lights to get them a few inches or so tall, and whether they turn out to be 2 inch or 4 inch is sort of irrelevant. My point is that if all you're doing is growing seedlings, don't waste your time worrying about the color of the light. But I do have to suspect that your success with fluorescents was largely with them keeping things warm. Growth rates are strong functions of temperature within a suitable temperature range.

Thanks!

Just a couple of weeks? Not up here in the north. Depending on the plant, seedlings are on the light cart anywhere from 1 to 14 weeks; average is about 8.

Wow. Down here, at 70F, my cucurbits are out and running in two or three weeks. Peppers do take a month though. I guess it partly depends on how big you want them to be. My 9oz cups won't handle big stuff, though. But again, getting 70F is easy if you cover the setup and hold in the heat from the lamps. In January and February, my converted garage is 45-50F, so it works well. Of course, at "night", when the lights are off, the plants cool off. But that's what outdoor gardens do in the real world. Temperature is a major major issue in growing speed.

Yep, similar here with cucurbits -- usually about 4 weeks until I start hardening them off to the outside. Tomatoes are 8 weeks, peppers a little less. Some flowers need a long time -- I've had nierembergia going since mid-February, they won't be put outside until mid-May earliest.

3000K fluorescent bulbs are a poor light source for plants and provide low photosynthetic active radiation. 5000k is a much better choice and provides a higher intensity of active radiation plants absorb for photosynthesis. 5500K and 6000K bulbs are even better for the intensity of active radiation for plants in active vegetative growth but I've never found any locally and have no desire to order them when 5000K will do fine. Buy the 5000K bulbs and throw away the 3000K bulbs. And if your 5000K bulbs are several years old replace them because intensity drops over time of use.

True about incandescent and fluorescent bulb intensity dropping over time. The intensity of LEDs drop over their lifetime too, but their lifetime is ENORMOUS. As a result, don't bother to replace old LEDs.

Actually, the spectral absorption of chlorophyl is a little complicated. It strongly absorbs blue AND red light (and obviously reflects a lot of the green). About 30% more strongly for blue. So you need BOTH blue and red light. Red light appears to promote fruiting growth, and blue light tends to promote foliage growth. So I would be inclined not to call 3000K "poor". But again, if you're worried about how much light your plants are getting, at least outside, the main issue is clouds. Don't get much "daylight" with those. Of course, if you're concerned that your seedlings under lights aren't getting enough illumination, just keep the lights on a bit longer.

"But again, if you're worried about how much light your plants are getting, at least outside, the main issue is clouds."

UV light penetrates cloud cover. Of course, it's stronger without, but still...plants still get exposure to light on cloudy days. Regardless, the topic is inside lighting, and I do agree that 3000K light is not "poor", plants need light from the red through the blue spectrum through the UV spectrum. Hence why I think plants do well with a mix of "warm" and "cool" bulbs. This whole thread has me tempted to switch out half my bulbs for "warm" LED tubes and see what happens. Except they're kind of expensive, so maybe just on one shelf (2 tubes). That still doesn't address the lack of heat output, though.

True. As I said below, a cloudy day is the color equivalent of 8000-1000K. Lots bluer than daylight. But not much light. The luminous intensity under a cloudy sky is maybe 10% that of a clear sky. Pretty much for any color. UV light largely does NOT penetrate cloud cover, though it penetrates a bit more than red light. I should add that if UV penetrated clouds, you'd get sunburned on cloudy days. You don't. This business of how many hours of sun you get needs to be modulated by how many hours of clouds you get.

Dan funny you mention daylight. I love daylight bulbs for decor in my house and my rehabs. I paint walls grey and soft white light (I call it piss light because it is so yellow) looks bad. I painted my girls bathroom from beige to grey. It looked better. Then I switched the bulbs from soft white to daylight. That made the bathroom look better then the paint job! They are brighter and go really good with grey paint.

My wife hates "daylight" bulbs. The whiteness is kind of striking to her. So I'm surrounded by "soft white". So it goes. I can imagine that painted surfaces look somewhat different with the different spectra.

I've notice there may be some misconceptions about Florescent lights. All kelvin temperature bulbs must emit blue, green and red light in certain ratios or otherwise we wouldn't get white or yellow light, and the only difference is the ratio or intensity of the different wavelengths.

Technically 3000K or 5000K florescent bulbs alone will grow seedlings OK because both have a sufficient intensity level of blue and red, but 5K lights have more blue while 3K have more red. Plant seedlings will benefit more from higher levels of blue light and grow stronger and healthier stems and seeds, but only during the seedling stage which lasts from germination to a few weeks after, and this is why I said 3000K was a poor choice for seedling.

After the seedling stage more red is required and the ratio is actually 4 parts red and 1 part blue, or 4:1. This is the ratio mostly used in commercial greenhouses and somewhat emulates the ratio as an average of the sun throughout the entire day, If after the seedling stage you want your plants go grow faster research and studies have proven adding far right red light in with a peak of 730 um will increase size from 30% to 70% depending on the amount, and believe Dan covered this.

Dan soft bulbs are definitely softer on the eye. I like bright lit rooms and with the color scheme of grey walls, white trim and dark oil rubbed bronze or black door hardware it looks great.

I do see how many would like soft light. Turning on the light in my house is like a shot of espresso in the AM:)

Good info here - thanks! REALLY good info.