You’ve found the right grow light.
You’ve positioned it near your plant.
Now comes another common question:
How long should you leave a grow light on each day?
For many indoor plants, you’ll often see recommendations somewhere between 8 and 16 hours.
But just like grow light distance, there isn’t one perfect number for every plant and every home.
A Monstera in a bright living room beside a window has a very different lighting environment from the same plant growing in a dark interior corner.
At GLOWRIUM, we prefer to think about grow light duration as part of a bigger picture:
Light intensity + light duration + natural daylight + plant needs
Understanding how these factors work together can help you create a much more useful lighting schedule.
Quick Answer: How Long Should Grow Lights Stay On?
For many of the common houseplants covered in GLOWRIUM's plant-lighting reference material, a useful reference range is:
12–14 hours of light per day
Some plants and growing stages may benefit from longer schedules.
For example, our reference material recommends:
| Plant | Recommended PPFD | Light Duration |
|---|---|---|
| Snake Plant | 100–150 μmol/m²/s | 12–14 h |
| ZZ Plant | 120–180 | 12–14 h |
| Rubber Plant | 150–200 | 12–14 h |
| Monstera | 150–250 | 12–14 h |
| Fiddle Leaf Fig | 180–250 | 12–14 h |
| White Bird of Paradise | 230–300 | 12–14 h |
| Basil, Oregano, Thyme | 250–300 | 14–16 h |
| Rosemary | 300–400 | 14–16 h |
| Seedlings | 120–180 | 14–16 h |
The large-houseplant ranges come from the room-corner and Monstera sections of GLOWRIUM's reference material, while seedlings and herbs are listed with longer recommended durations.
But there's an important distinction:
“12–14 hours of light” doesn't always mean “run your grow light for 12–14 hours.”
Natural daylight counts too.
Grow Light Hours vs. Total Light Hours
Imagine two Monsteras.
Monstera A
It sits beside a bright window and receives useful natural daylight for several hours.
Monstera B
It sits in an interior living room corner with very little natural light.
Both are Monsteras.
But their grow lights may not need to operate for exactly the same amount of time.
Why?
Because the grow light is only one part of the plant's total daily light environment.
A useful way to think about it is:
Natural Daylight + Supplemental Grow Light = Daily Light Environment
If natural daylight already contributes significantly, the grow light can supplement it.
If natural daylight contributes very little, artificial lighting may need to play a much larger role.
Why Light Duration Matters
Plants use light to drive photosynthesis.
But the amount of light a plant receives over a day isn't determined only by how bright the light is at one moment.
Time matters too.
A plant receiving appropriate light for several hours experiences a different daily light environment from one receiving that same intensity for a much longer period.
That's why indoor plant lighting involves two related questions:
How much light reaches the plant?
This is where measurements such as PPFD become useful.
And:
How long does the plant receive that light?
That's where your lighting schedule comes in.
Neither number tells the entire story by itself.
PPFD and Light Duration Work Together
PPFD stands for Photosynthetic Photon Flux Density.
It describes the amount of photosynthetically active light reaching a given area each second.
But PPFD is an instantaneous measurement.
It tells you what is happening at that moment.
Plants experience light over an entire day.
This leads us to another useful concept:
What Is DLI?
DLI stands for Daily Light Integral.
If PPFD tells you how much photosynthetically active light is arriving right now, DLI describes the accumulated amount received over the course of the day.
Conceptually:
PPFD × Time = Daily Light
This is why intensity and duration shouldn't be treated as completely separate decisions.
A lighting schedule makes more sense when you know approximately how much light the plant receives while the light is on.
How Long Should a Grow Light Be On for Monstera?
For standard Monstera, GLOWRIUM's reference material recommends:
PPFD: 150–250 μmol/m²/s
Light Duration: 12–14 hours per day
If your Monstera is in a darker corner, supplemental lighting may need to contribute more heavily to that daily period.
If the plant is already receiving substantial natural daylight, your grow light may function primarily as supplemental lighting.
This is why simply copying someone else's timer schedule isn't always the best approach.
Their Monstera may be growing in completely different conditions.
How Long Should a Grow Light Be On for Fiddle Leaf Fig?
Our reference material recommends approximately:
PPFD: 180–250 μmol/m²/s
Light Duration: 12–14 hours per day
Again, that doesn't automatically mean:
Turn the grow light on for exactly 14 hours every day.
Start by considering the amount of natural daylight reaching the foliage.
A Fiddle Leaf Fig beside a large window and one sitting deep inside a room shouldn't automatically be treated as identical lighting situations.
How Long Should a Grow Light Be On for Bird of Paradise?
White Bird of Paradise has one of the higher recommended PPFD ranges among the large plants in our reference material:
PPFD: 230–300 μmol/m²/s
Light Duration: 12–14 hours per day
This is particularly important because Bird of Paradise is often used as a large statement plant.
It may look beautiful in an empty corner—but that location may receive limited daylight.
If natural light is insufficient, artificial lighting may need to make a larger contribution to its daily light environment.
Do Low-Light Plants Need Fewer Hours?
Not necessarily.
This is an easy mistake to make.
A plant with lower light requirements doesn't automatically need only a few hours of light.
Look at the ranges in our source material:
Snake Plant: 100–150 μmol/m²/s for 12–14 hours
ZZ Plant: 120–180 μmol/m²/s for 12–14 hours
The main difference here is intensity, not necessarily a dramatically shorter daily schedule.
So don't think:
Low-light plant = very few hours of light.
Instead think:
Different plants can require different combinations of intensity and duration.
Should Grow Lights Be On All Day?
They can operate for a substantial portion of the day when appropriate.
But that doesn't mean they should remain on continuously.
For many of the houseplants in our reference material, 12–14 hours provides a useful reference schedule.
That leaves approximately:
10–12 hours of darkness
within a 24-hour cycle.
A regular dark period is part of the plant's normal day/night environment.
So:
More hours ≠ automatically better.
Should Grow Lights Be On 24 Hours a Day?
For the plants covered in our source material, no 24-hour lighting schedule is recommended.
The reference schedules are generally 12–14 hours for foliage houseplants and 14–16 hours for seedlings and certain herbs.
Leaving a grow light on continuously also wastes energy when those extra hours aren't part of the intended lighting plan.
Instead, build a consistent light/dark cycle.
Is It Better to Run Grow Lights During the Day or at Night?
For most home setups, running supplemental grow lights during normal daytime hours is usually the simplest approach.
For example:
Natural daylight begins in the morning
↓
Grow light supplements during the day
↓
Grow light turns off in the evening
↓
Plant receives darkness overnight
This also makes grow lights easier to integrate into living rooms, bedrooms, and home offices.
At GLOWRIUM, we think this matters.
A grow light in a home isn't operating in isolation.
It's part of the space you live in.
What Time Should Grow Lights Turn On?
There isn't one required clock time.
Consistency is more useful than obsessing over a specific hour.
For example, a schedule might be:
7:00 AM → 7:00 PM
or
8:00 AM → 8:00 PM
depending on the plant, natural daylight, season, and your household routine.
The important point is that the schedule should fit the plant's intended light period and preserve a regular dark period.
Why a Timer Is Useful
You probably don't want to manually switch a grow light on every morning and off every evening.
A timer makes the routine consistent.
This becomes particularly helpful when:
- You have several plants
- You travel
- Your work schedule changes
- The grow light supplements winter daylight
- Your plants are in different rooms
Once you've established an appropriate schedule, automation removes one more thing from your daily routine.
For GLOWRIUM grow lighting, this is one reason timer and scheduling functions can be genuinely useful—not simply convenient features.
Should You Change Grow Light Hours in Winter?
Possibly.
Indoor natural-light conditions can change considerably across seasons.
During winter:
Days may be shorter.
The sun's position changes.
Some rooms receive less usable daylight.
A plant that receives sufficient natural light during summer may therefore depend more heavily on supplemental lighting during winter.
Instead of automatically using the exact same grow-light schedule year-round, periodically reevaluate the actual conditions around the plant.
Ask:
How much natural light is reaching this plant now?
Your supplemental lighting schedule can respond accordingly.
What About Windowless Rooms?
A windowless room changes the equation considerably.
There may be little or no meaningful natural daylight contributing to the plant's daily light environment.
In this case, artificial plant lighting may need to provide most of the usable light.
That's very different from supplementing a plant beside a sunny window.
This is another reason generic recommendations like:
“Run your grow light for six hours.”
aren't particularly useful without context.
Six hours of what intensity, for which plant, in what environment?
Those details matter.
How Do You Know If Your Schedule Is Right?
Don't evaluate only the timer.
Evaluate the entire system.
Check PPFD
How much usable light reaches the canopy?
Check Duration
How long does the plant receive that light?
Consider Natural Daylight
How much is the window already contributing?
Watch the Plant
Growth and overall plant condition can help you determine whether the environment needs adjustment.
Reevaluate Over Time
Plants grow.
Seasons change.
Furniture moves.
Your lighting setup should be allowed to change too.
A Simple Grow Light Schedule for Large Indoor Plants
For the large houseplants we've been covering in this GLOWRIUM series, a useful starting framework is:
Step 1 — Identify the plant
Know its approximate PPFD and duration recommendations.
Step 2 — Evaluate natural light
Bright window or dark corner?
Step 3 — Measure at canopy level
Determine what actually reaches the foliage.
Step 4 — Add supplemental lighting where needed
Don't automatically replace useful natural light.
Step 5 — Build a consistent schedule
For many of these large foliage plants, use 12–14 total light hours as the reference from our source material.
Step 6 — Preserve darkness
Don't leave the light running 24/7.
Step 7 — Adjust as conditions change
Especially across seasons or as the plant grows.
Light Intensity and Time Belong Together
The question:
“How many hours should I leave my grow light on?”
sounds simple.
But the better question is:
“How much light does my plant need across the entire day?”
That's the difference between thinking only about a timer and thinking about the plant's actual lighting environment.
At GLOWRIUM, our approach is to bring together:
Plant needs
PPFD
Duration
Natural daylight
Placement
Coverage
Because good plant lighting isn't about turning a lamp on for an arbitrary number of hours.
It's about giving the plant the right amount of light, over the right amount of time.
FAQ: Grow Light Hours
Is 12 hours of grow light enough for indoor plants?
It can be appropriate for many indoor plants, depending on light intensity, species, and natural daylight. Our reference material recommends 12–14 total light hours for many common foliage houseplants.
Is 8 hours of grow light enough?
Possibly, if useful natural daylight contributes to the rest of the plant's daily lighting environment. Duration shouldn't be evaluated without considering intensity and natural light.
Can I leave my grow light on for 16 hours?
Our reference material recommends 14–16 hours for seedlings and several herbs, while many foliage houseplants are listed at 12–14 hours.
Should grow lights be turned off at night?
The schedules in our source material all include a daily dark period rather than continuous 24-hour lighting.
Do grow lights need a timer?
A timer isn't essential to photosynthesis itself, but it makes maintaining a consistent daily schedule much easier.
Does natural sunlight count toward grow light hours?
Yes. When evaluating a plant's overall lighting environment, useful natural daylight should be considered alongside supplemental artificial light.
