How Many Watts Should My Grow Light Have?

Views: 13     Author: Site Editor     Publish Time: 2022-06-14      Origin: Site

How important is it to have a grow light when growing indoor plants? It depends mostly on the type of plant you're growing but also on what you're trying to achieve. Low-light indoor plants will do fine on a sunny windowsill. However, coaxing plants to bloom, raising fresh herbs, and starting seedlings require brighter and more consistent amounts of light.

Indoor Plant Growth Light

It all depends on what you're growing. Spider plants couldn't care less if they lived in a closet. On the other hand, jade plants need at least four hours of direct sunlight daily to thrive. Different plants have different light requirements. The first step is determining how much light your plants will need to thrive.

Next, you need to figure out how many watts your lights should have. The optimal number of watts per square footage ranges from 20 – to 40 watts. Therefore, for a 10-foot grow room, you will need between 200 – 400 watts of light. Keep in mind that these are the extremes of your setup's required light range. Always adjust based on what your fixed setup can handle. For example, do not get ten 40-watt bulbs when your setup only needs 250 watts.

Buying Grow Lights – What You Need to Know

Types of Grow Lights

There are two types of indoor plant growth lights to consider:

  • Fluorescent bulbs

  • LED bulbs

Fluorescent bulbs are the older technology. They are cheaper and more efficient than incandescent bulbs. However, some are manufactured with mercury and pose significant safety hazards due to their fragility.

LED bulbs are more efficient and last up to five times longer than fluorescent bulbs. They convert up to 95% of the energy input, wasting only 5% on lost heat. Their only caveat is that they cost more upfront.

It depends on how much electricity your setup consumes. With a small collection of indoor plants, spending on LED lights may be cheaper and will save electricity. Fluorescent bulbs may be ideal if you’re not too concerned about consumption, but you should always try to invest in the latest technology.

Case in point, some LED lights are specially made to grow plants. They are labeled as 'grow lights' and can sometimes be specified by the type of light waves they produce. Red light waves, for example, are preferred for growing indoor plants.

Best Lights for Different Results

There are many types of grow lights out there, ranging from cheap regular LED bulbs to special LEDs designed specifically for growing plants. It's best if you first figure out your light requirements before buying anything.

Your light requirements will be determined by the plant type and its current development stage. Seedlings need very different light from flowering plants, and this also varies by plant species.

Similarly, plants that thrive in very specific environments (for example, cacti in semi-arid areas) need to be treated accordingly and given as little or as much light as they need.


Newly emerged seedlings need large amounts of full-spectrum light. Full-spectrum light contains both red and blue wavelengths. You will find plenty of affordable LED bulbs that produce a decent amount of full-spectrum light. A standard seedling nursery must have the lights suspended at least 6 inches from the plant foliage.

Flowering Plants

Grow lights that emit a high number of red-light waves are specially reserved for flowering and fruiting plants. If you're looking to induce flowering or increase the fruit yield of a specific indoor plant, shop for LED bulbs that are specifically labeled as “grow lights.”

Plants from Dry Climates

Plants that thrive in sunny, dry climates like rosemary and geranium will do best under a high-output LED grow light. These are generally twice as bright as standard LED's and thus the best for replicating the sunlight in arid climates. Such plants will need light for up to 18 hours a day, with the light source at least 12 inches away from the foliage.

Water Plants

Did you know there are grow lights for water plants too? Nothing can stop you from keeping your favorite hydro plants, particularly since they don't have very high light requirements.

Again, consider the size of your setup to determine what kind of lights you need. In any case, most plant lights are already configured to deliver the right amount of light to plants that thrive underwater.