LED bulbs have a full color spectrum. Therefore, they are usable for specialty purposes such as illuminating indoor gardens.
Full spectrum means that the bulb emits light across the entire visible spectrum hence nearly similar to natural sunlight.
Such LED lights promote photosynthesis and therefore indoor plant growth thanks to near perfect natural light mimicry.
In other words, such LEDs have a high color rendering index (CRI) of at least 90% meaning that their light is nearly equivalent to natural sunlight.
Some LEDs even hit CRI values as high as 95-98, which is an exceptional approximation of the full spectrum of natural sunlight.
What You Should Look for in an Ideal Grow Light
Light Output (PPF)
LED grow lights should produce light spectrum within the photosynthetically active radiation (PAR) range (400-700 nm).
Why is PAR range important? Plants require varying light spectrums at different growth stages – seedling, vegetative, flowering, fruit & seed development.
The table below shows the different light wavelengths required at the 4 stages, and their impact.
| Plant Growth Stage | Seedling | Vegetative | Flowering | Fruit & seed development |
| Required light spectrum & wavelength in nm | Blue (400-500) | Blue (400-500) & Red (600-700) | Mostly red light (600-700) | Blue (400-500), Red (600-700), & far-red (700-800). |
| Purpose |
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As you have seen, specific light spectrums are required at particular growth stages.
However, you shouldn’t worry about how to apply them when using full spectrum LED grow lights.
Why? LED grow lights are designed to cover all these light spectrums out of the box.
Photosynthetic Photon Flux (PPF) is the metric that measures light output level of grow lights.
PPF especially measures a grow light’s photosynthetically active photons (within PAR range) in µmol/s (micromoles per second).
Takeaway:
A higher PPF value is better than a lower PPF value since it means more usable photons.
However, this metric matters little considering that mounting heights vary (read on light intensity below to understand better).
Light Intensity (PPFD)
PPFD means photosynthetic photon flux density and it shows the amount of light striking a unit area of a plant canopy – measured in µmol/m²/s (micromoles per square meter per second).
It’s calculated as PPF (µmol/s) to the specific area (m²) ratio.
PPFD is a metric that is usually adjusted in the different stages of plant growth.
For instance, the seedling, vegetative, and flowering stages require PPFD value ranges of 100-300, 400-600, and 800-1000 µmol/m²/s respectively.
Most critically, you should know that PPFD depends on 2 main factors – a lamp’s PPF, and its mounting height.
A lamp’s mounting height affects its beam distribution. A higher mounting height spreads photons over a larger area while a lower mounting height spreads photons over a smaller area, thus reducing the PPFD.
While maintaining a lamp’s mounting height constant, one can equally vary its PPFD by dimming its light output (PPF) – this is a quicker technique for varying PPFD because it involves using a dimmer switch instead of physical lamp height adjustment.
Some manufacturers provide PPFD maps showing light intensity at different heights (see image below).
You will notice the middle part has higher PPFD values. This is because it is directly above (or perpendicular) to a grow light.
If a grow light is dimmable, you may find a specification showing how the PPFD varies at different dimming levels but at fixed heights (see image below).
Takeaway:
Look out for lamps that have a high PPFD value of about 800-1000 µmol/m²/s at a mounting height of 1 foot (12 inches).
It’s even better if you find a dimmable grow light. Remember, dimmability provides PPF adjustment, hence effortlessly varying PPFD at a fixed lamp height.
Energy efficiency (PPE):
Photosynthetic photon efficacy (PPE) measures a grow light’s energy efficiency showing how efficiently it converts electrical energy into usable photons, expressed in µmol/J (micromoles per joule of energy).
It’s calculated as the ratio of lamp’s PPF to power use, i.e., µmol/s ÷ J/s = µmol/J.
Higher PPE values mean more energy efficient grow lights which have higher cost savings and better performance.
High quality lights feature PPE values > 2.0 µmol/J, less efficient LEDs are in the 1.5-2.0 µmol/J range, while traditional non-LED grow lights have lower than 1.5 µmol/J.
Takeaway:
Aim for grow lights with at least 2.0 µmol/J.
Coverage area & Uniformity
A grow light should be installed in a manner to provide a uniform coverage of indoor plant foliages.
It’s encouraging to know that grow light manufacturers specify the ideal plant coverage areas that grow lights provide. Such a recommended coverage area is seen in the image below.
Takeaway:
Buy one or more grow lights that sufficiently cover your indoor growing area.
If you use lights to illuminate a larger growing area than recommended, then the plant growth will be sub-optimal.
Lifespan
Modern high quality LEDs last tens of thousands of hours, guaranteeing 25,000-50,000 hours of useful life.
The key takeaway here is that you needn’t worry about the lifespan factor as long as you’ve bought a high quality grow light from a reputable brand.
Dimmability
Under the light intensity (PPFD) factor, you have already read that a dimmable grow light is an advantage, allowing easy light output (PPF) adjustment to achieve a desired PPFD level.
Why is dimmability critical?
It provides a hassle-free method of achieving various light intensity levels required at different plant growing stages unlike lamp height adjustment.
Besides, it provides enormous energy saving compared to height adjustment since dimming reduces actual energy use while height adjustment retains full light intensity hence no energy savings.
Takeaway:
Always buy dimmable grow lights over non-dimmable counterparts when you have the option.
Waterproofness
If you’re going to use grow lights in high humidity environments, it’s important to buy waterproof variants. Look for waterproofness in dimmers too!
The waterproofness of a product is known technically as Ingress Protection rating. Look out for it in the product information.
Look for grow lights/dimmers with either IP65 or IP67 rating. IP65 lights are resistant to dust and water jets while IP67 means ability to handle temporary immersion.
Ingress protection is an essential consideration when buying grow lights and dimmers.
Why? Firstly, to ensure moisture damage protection, and secondly, minimizing risks of electrical hazards, both of which ascertain product durability and safety.
Takeaway:
Buy lights have a good IP rating to guarantee that they are durable and safe to use especially in very humid environments.
