One of the most common questions I field is what we use for lighting. Lighting is an absolute non-negotiable for all our indoor seed starting. There’s just no good way to produce healthy and strong plants without supplemental lighting.

Because we have repurposed existing lights, I will share our current lighting setup and the types of lights we use and their strength. I admit it’s a bit of a rat’s nest, sorting through lighting options online. My husband spent weekends, plural, taking notes and scouring lighting companies to find the right level of brightness to mimic our tried and true fluorescent system.

Our grow lights currently include a combination of 4-bulb T8 fluorescents, 4-bulb T8 LED equivalents, and one full spectrum LED.

Our T8 compact fluorescent lights have 2 types of bulbs: a 6500 bright white and a 3500 cool white bulb, blending the blue and red light needed to emulate the full spectrum plants need.

Fluorescent lights (top shelf) vs LED replacements (bottom two). Notice the relative distance of plants to lights between the two.

For the first 20 years of our gardening career, we successfully grew under our 4-bulb, 4-foot T8 shop lights with half cool white and half bright white (fluorescent) 32W bulbs. We purchased these at a big box home improvement store. Each fixture cost $60, plus about $50 more for lights. For each light fixture, we have the capacity to grow 2, 1020 trays, or larger plants that fit in those trays (like 16 tomato plants potted up).

We did have a T5 fixture for a few years early on, but the bulbs were more expensive to buy and we were frugal. Knowing our less expensive lights did the same job for us, we stopped using it. (If I’m recalling correctly, it also broke and was out of warranty.)

So the simpler, fluorescent lights were a tried and true method for so long that it’s been hard to shift our mindset away from something that works so well. However, as the bulbs have started to die out, it’s been an opportunity to question if we continue with fluorescents or try to re-purpose the lighting unit and transition to LEDs.

We have 12 shelves in total, across 4 plant stands of varying height and capacity. One stand rarely gets fully used, unless we are doing a lot of perennial germination like for our burgeoning native edible food forest. Two stands with 3 shelves each have adjustable light heights up to 2 feet per shelf (as seen above); they are the most flexible of all the stands due to the amount of height they can accommodate, and thus the most used. The lights are on chains and eye hooks above allow for easy height adjustment, which sometimes occurs several times a week. The newest shelf was a test: it has four shelves, each with less vertical play, a design I thought would be great for things like brassicas and flowers that are only indoors for a short period of time. But it presents a challenge when growing under LED lights. I’ll explain more below.

The old system is familiar: keep the plants hugging the lights until we start hardening them off.

In the past five years, we also saw the lifespan of many of the bulbs sunset and the need to replace them became clear. We knew it was the right time to try LED bulbs in these light fixtures. In order for LED bulbs to work in these fluorescent fixtures, you may need to remove the ballast, which controls the amount of electricity flowing through the bulb. LEDs don’t operate on a ballast. The bulbs we purchased are a ballast bypass type, so my handy husband leaned on his trusted you tube surfing skills to help remove the ballast so the bulbs would work with the existing fixtures. Each new light cost about $10 each. And now about half of our old 4-bulb fixtures are running on LED lights.

This ballast setup will be different for each type of light fixture, but if this is something you’re interested in doing, it’s a quick you tube search to find the right fixture. Here’s how we bypassed our Sylvania fixtures. Surely someone out there has done it for your fixture and posted how to do it, I can guarantee. Thank you, internet.

The Numbers

The key for growing indoors is finding lights as bright as possible. Even the brightest lights won’t come close to a sunny outdoor day, but our plants are forgiving and grow anyway.

For LED purchases, you want to find the Kelvin. This is the brightness of the color. Kelvin between 5,000-6,500 is ideal for vegetative growth, which is what we are doing inside our homes in late winter preparing our plants for summer’s flowering (hello, tomatoes and peppers!).

This turns out to sometimes be a wild goose chase. Information isn’t always presented in the way we need it. So, to possibly save you some time running around in circles on your time off, here are the bulbs we currently use in our fluorescent light fixtures.

Replacement Bulbs

For our old T8 fixtures, here are the LED ballast bypass bulbs we are currently using. We use 2 of each in the fixtures, alternating them so each side has one of each.

Like with our old system, they are half “cool white” and half “bright white”, thus combining to create as full a spectrum as possible:

LED Daylight equivalent: https://www.bulbs.com/product/KT-LED15T8-48GC-865-DX2?cm_mmc=GooglePLA-_-Nonbrand-_-16389752855-_-shopping&affID=6&gclid=EAIaIQobChMI3NvisJba9gIVjCtMCh1MeAuLEAQYAiABEgLbE_D_BwE

LED Cool White equivalent: https://ecoledmart.com/products/led-tube-ballast-bypass-4ft-22w?variant=12032894402602

If you have fluorescent fixtures and want to stick with them (we love ours still!), here are the reliable bulbs we are still using in over half our light fixtures. Like with the rest, we use 2 each of these and alternate them in the fixture.

T8 Fluorescent Cool White: https://www.homedepot.com/p/Philips-32-Watt-4-ft-Linear-T8-ALTO-Fluorescent-Tube-Light-Bulb-Cool-White-4100K-2-Pack-543306/308644136

T8 Fluorescent Daylight: https://www.homedepot.com/p/Philips-32-Watt-4-ft-Linear-T8-ALTO-Fluorescent-Tube-Light-Bulb-Daylight-5000K-2-Pack-543314/308644340

New in 2024:

I ordered some Sunlite T8 lights from Gardeners Supply last year. They replaced 3 of our oldest fixtures’ T8 cool white and daylight bulbs. They only come in one brightness (2850 lumens, 94% of full spectrum) but are supposed to be 20% more efficient and last longer, both bonuses for these fixtures that aren’t as energy efficient as our LED ones. Unfortunately, they are not currently in stock on their website!

Full Spectrum LEDs:

In 2019, we also dipped our toes into the world of full spectrum LED lights. We went with the Roleadro 300W LED light. It looks like while searching amazon (where we picked this up for $60) that it’s no longer available and they carry a 600W or 1200W one now. I searched the internet and only found our fixture offered second-hand through eBay. I find the fleeting nature of products these days so challenging — many of the items I recommend are not currently available. I am sorry about that!

This 300W LED light sits in a fixed position as high up as possible, and the plants seem ok. It’s a strange thing to have only one, smaller light fixture for a 2’x4’ space. But, it works!

We keep the lights on 24/7 once seedlings emerge to maximize vegetative growth. This is quite an unusual approach in the home gardening world, but it has always worked for us so we continue to roll with it. Our home does take on a suspicious glow from March - May at night, but it’s all legal.

When to Replace Your Lights

This is an important question to ask yourself. When was the last time you replaced your bulbs? I like to add blue tape and the year I replaced the bulbs on my fixtures so I know when we replaced the bulbs. In general, I try to replace mine every 4 years or so.

You can also look for a darkening of the ends of the fluorescent bulbs as an indication that it’s time to replace them. And, using a light meter will also help you know when they are fading.

Measuring Your Lights

Another way to know how strong your lights are is to measure the light with a light meter. This was discussed in last month’s Q&A but is worth noting here too.

An MGG member a few years ago told me about a light meter to use and I bought one off Amazon (links to my affiliate page). It does seem to work on both fluorescent and LEDs, which was something I was asked about last month.

My light meter reading our LED replacement bulbs. The white bulb is the light sensor. This value needs to be multiplied by 100 to get its Lux value. At 26,000 Lux, this LED replacement is putting out on the high end of daylight (though the very low end of direct, bright sunshine) when measuring about an inch or two below the lights.

I set the meter to lux (stands for Luminous Flux). Foot Candles are the other metering option; Foot Candles are like what feet are to meters. FC’s are used in the US and Lux seems to be the worldwide standard.

I use the x100 metering function, which I get to by pushing the range button until I see an x100 on the screen. So when I see a number like 200, it means 20,000 lux.

Here are some values to consider:

Overcast day: ~1,000 lux
Daylight: 10,000-25,000 lux
Direct sunlight: 32,000-130,000 lux

This is a great way to get data and understand your lights. You will be able to see how the intensity drops as you move the meter further away from the light. For our LED replacements, the light is a bit stronger up close and so I can keep them a little further away from my plants compared to the regular T8 fluorescent bulbs.

Light Height: The Key to Strong Starts

The other big question I get asked often from friends who start their plants indoors is why aren't ours leggy. And the answer is simple: with fluorescents, you must keep your plants as close to the fixture as you can because the light doesn't penetrate very far down. How close do you keep your light to your plants? If they are fluorescents like ours, keep the light as close to the plants as possible without touching. For these lights, the cage of the fixture is usually just about touching the plants. The light won't burn the plants, so don't worry about that, and bringing the light to them eliminates the plants' need to reach up for the light since this light is not as strong as T5s or high output grow lights. For us, at the end of the day, we are successful enough with this system to not justify the additional cost of the new fixtures and bulbs.

With LEDs, the plants must be kept farther away from the lights, which runs in complete opposition to what we are accustomed to — this is the hardest part of the change.

The other thing that is quite different with LEDs is that generally you need to keep your plants much farther from the light than fluorescents. Fluorescent light diminishes rapidly in the first few inches, so in order for the light to do its job as a proxy for sunlight, you have to keep the lights practically touching the plants. LEDs are completely different.

I am still getting accustomed to how far away to keep the LEDs. Couple that with our fixed height of our plant stands, and we have a bit of a challenge with larger plants like our tomatoes and peppers that get quite large come mid-April. That is the largest and next big learning curve for me, to really push the height in both directions for starts growing under LEDs.

And as I said earlier, it’s really hard to experiment on your actual plants for the coming growing season. I mean, which one of us has time to play with a few extra trays for the sake of science? I did a little last winter for the book, but right now, I must learn in real time with actual plants, some of which don’t have backups. Such is life.