In this section:

• Introduction
• Types of Grow Lights
• Kelvins vs Lumens vs PAR vs µmol/J: Understanding Light Measurements
• Watts: Power Consumption vs Efficiency
• Light Spectrum and Plant Life Stages
• Choosing the Right Light for Your Indoor Grow
• Green’s Quality Standard
• Brand Overview (A-Z)

Choosing the right grow lights for your indoor plants is essential for healthy growth and high yields. The type of light, spectrum, intensity, and efficiency all play a role in supporting plants through different stages of their life cycle. Whether you're a hobbyist growing herbs on a windowsill or a dedicated indoor gardener cultivating vegetables or flowers, this guide will help you make an informed decision.

Outdoors, plants use light from the sun to help them flourish. Sunlight has a wide spectrum and plants have to use a specific window of the wavelength range of light (400 – 700 nanometres, in case you were wondering) to carry out photosynthesis (the process which they use to convert light energy into the essential sugars needed to grow and survive).

In the scientific field, this wavelength window is known as Photosynthetically Active Radiation (PAR for short), and it’s this range that you need to replicate indoors in order to mimic sunlight and provide the perfect environment to grow quality, healthy crops.

Furthermore, plants respond differently to the wavelengths of light within the PAR window. Different wavelengths correspond to the plant growth cycle's vegetative and flowering/fruiting stages. Grow lights are purposefully designed to accommodate for all stages of the plant's growth cycle, which is why carefully choosing the right grow light matters.

Types of Grow Lights

There are three main types of grow lights in the horticultural industry; Compact Fluorescent Lights (CFL), High Intensity Discharge (HID) lights, and Light Emitting Diode (LED) lights. The industry has made some positive advances recently: energy-efficient LED units now have the potential to outperform all existing methods AND are affordable. A big win for growers and our lovely planet. On top of this, CFLs are being phased out due to their harmful mercury content. For those still using CFL, read on to find out about the more energy-efficient and environmentally friendly lighting technologies (such as LED) that you can benefit from when you’re ready for the switch. You won’t regret it!

Propagation Lights
For seedlings and cuttings, low-intensity lights like T5 fluorescent tubes (CFL) or LED propagation lights provide gentle illumination to encourage root development without stressing young plants.

LED Grow Lights
LED (Light Emitting Diode) grow lights have revolutionised indoor gardening, providing an energy-efficient, long-lasting, and highly customisable lighting solution for plants at all growth stages. Whether growing herbs on a kitchen windowsill, nurturing houseplants, or cultivating vegetables and flowers in a grow tent, LEDs offer a practical and effective alternative to traditional lighting methods. They generate less heat, reducing the risk of scorching plants, and are available in full-spectrum or adjustable-spectrum models for healthy, vigorous growth from seedling to harvest. For most UK growers, LED grow lights are the best option due to their efficiency, longevity, and ability to support plants throughout their full life cycle. While the initial cost can be higher, the potential savings in electricity, cooling, and bulb replacements make them a worthwhile investment for both hobbyists and commercial growers alike.

Pros:

• Watt for Watt, LEDs are significantly more energy-efficient than traditional High-Intensity Discharge (HID) lights such as Metal Halide (MH) and High-Pressure Sodium (HPS), reducing running costs.
• Many LED grow lights offer full-spectrum output, meaning they can support plants from seedling to harvest without needing to switch bulbs. Some models even allow spectrum adjustments to optimise vegetative growth (blue light) or flowering (red light).
• Unlike HID and fluorescent lights, LEDs produce very little heat, reducing the risk of plant damage and allowing lights to be positioned closer to the canopy without burning foliage. This also means less need for additional cooling or ventilation.
• High-quality LED grow lights can last 50,000 hours or more, far outlasting HPS, MH, or fluorescent bulbs, which degrade more quickly and require frequent replacements.
  Many modern LED grow lights come with dimmable settings, programmable timers, and spectrum controls, allowing growers to fine-tune lighting conditions for different plant stages.

Cons:

• Although LED grow lights save money in the long run through energy efficiency and durability, the upfront investment can be higher compared to traditional lighting.

High-Intensity Discharge (HID) Lights
HID lights, such as Metal Halide (MH) and High-Pressure Sodium (HPS), have been popular among commercial growers. MH bulbs are best for vegetative growth, while HPS bulbs promote flowering and fruiting. However, they consume more energy and produce more heat than LEDs. HID grow lights need a ballast to operate and are available in a range of wattages, from 150W all the way to 1000W of power, meaning they can be used in practically any sized growing environment. When used in the right-sized, adequately vented environment, the correct HID light will provide great light intensity that penetrates the entire growing space, helping plants stay healthy from the bottom of the stem to the tip of the highest leaf.

Pros:

• Strong light intensity makes them highly effective in terms of results
• Replacement bulbs for HID lamps are cheaper to purchase than alternatives
• Traditionally most-popular, highly reliable technology

Cons:

• Less energy efficient than LEDs
• Output more heat per watt than LED or CFL and can be unsuitable for smaller growing environments, or in hotter climates

Kelvins vs Lumens vs PAR vs µmol/J: Understanding Light Measurements

In the world of horticultural lighting you may come across several unfamiliar words:

Kelvins (K) measure the colour temperature of light. Cool white light (5,000–6,500K) mimics daylight and is ideal for vegetative growth, while warmer light (2,700–3,500K) is better for flowering and fruiting plants.

Lumens (lm) measure the brightness of a light source but don’t indicate its suitability for plant growth. Instead, Photosynthetically Active Radiation (PAR) is a more useful measurement, as it represents the amount of usable light for photosynthesis.

What is µmol/J and why is it Important?
When choosing an LED grow light, one of the most important efficiency metrics to consider is µmol/J (micromoles per joule). This measurement indicates how efficiently a grow light converts electrical energy into usable light for photosynthesis.
Photosynthesis Efficiency – As mentioned above, plants rely on light in the Photosynthetically Active Radiation (PAR) range (400-700nm) for growth. A higher µmol/J value means the LED produces more useful light per watt of energy consumed, ensuring plants receive adequate light for photosynthesis without excessive energy waste.

Energy Savings – A grow light with a high µmol/J rating produces more usable light with less electricity, leading to lower running costs over time. For example, an LED with 2.5 µmol/J is significantly more efficient than one with 1.5 µmol/J, providing better growth for the same power consumption.
Less Heat Production – More efficient LEDs generate less heat, reducing the need for extra cooling and allowing closer placement to plants without causing damage.
Higher Yields per Watt – Grow lights with higher µmol/J values deliver more photons to plants, resulting in stronger growth, increased yields, and healthier crops—especially important for flowering and fruiting plants.

What is a Good µmol/J Rating?
Basic Efficiency (1.5–2.0 µmol/J): Found in older or lower-quality LEDs. Suitable for small-scale growing but not ideal for high-yield setups.
Mid-Range Efficiency (2.0–2.5 µmol/J): Offers a good balance between affordability and performance. Suitable for home and hobbyist growers.
High Efficiency (2.5–3.5+ µmol/J): Found in premium, high-performance LED grow lights. These maximise light output while minimising energy consumption and heat.
Choosing the Right LED Grow Light
For UK growers looking to maximise efficiency and plant growth, choosing an LED with at least 2.5 µmol/J is recommended. High-efficiency LEDs may cost more upfront but will help to reduce electricity costs and improve plant health, making them a smart investment for long-term indoor gardening.

Watts: Power Consumption vs Efficiency

Watts measure energy consumption, not necessarily the light output. A higher wattage light isn’t always better for plant growth. LED grow lights provide more usable light per watt than HID or fluorescent bulbs, making them the most efficient option. Always check the PPFD (Photosynthetic Photon Flux Density) rating, which indicates how much light actually reaches your plants.

Light Spectrum and Plant Life Stages

Plants have three main stages in their growth cycle; the propagation stage, the vegetative stage, and the flowering/fruiting stage. Different spectrums of light are suitable for different stages of growth. Therefore, it’s highly important that you use the correct lighting for each of these stages to ensure your plants are growing to the best of their ability. Luckily, grow lights are available to suit all stages of the plant growth cycle.

• Propagation Stage: Blue-heavy light (5,000–6,500K) encourages leafy, compact growth. During the propagation stage plants are busy forming roots and building a solid foundation on which to grow and flourish. At this crucial stage, it is important that your seedlings or clones have gentler, lower-powered lighting to start them off. Too much light/heat can easily stress young plants. As less light energy is needed during the propagation stage than in the other stages of plant development, propagation lighting outputs little heat and can be placed close to your plants, ensuring healthy and sturdy growth.
• Vegetative Growth (Leaves & Stems): Again, blue-spectrum light (5,000–6,500K) but now you can look to start increasing both light intensity and power. LED grow lights and metal halide (MH) are both great options for vigorous, bushy, healthy growth. Dual spectrum lamps also offer good results at this stage.
• Flowering & Fruiting: Warmer, red-heavy light (2,700–3,500K) stimulates blooming and fruit production. High-Pressure Sodium (HPS) or full-spectrum LEDs are ideal.

Choosing the Right Light for Your Indoor Garden

• For houseplants and herbs, a simple LED or fluorescent light may suffice.
• For vegetables and fruiting plants, a full-spectrum LED with both blue and red light is ideal.
• For commercial or large-scale indoor grows, HID or high-power LED setups provide the best results.

By selecting the right grow light(s), you can ensure your plants receive the perfect balance of light intensity, spectrum, and efficiency to thrive indoors, no matter the season. By selecting Green’s, you can be sure you’re in knowledgeable, experienced, safe hands.

The Green's Quality Standard

We stock a wide range of grow light products here at Green’s, from entry-level value kits for novice gardeners to revolutionary lighting products for highly experienced growers. Although our products may differ to accommodate our range of diverse customers, our commitment to quality stays the same across our product range. All grow lights on our site come from reputable brands, they are all CE certified, and most importantly, they all meet our strict quality standards. We make sure we never settle for second best, so you don’t have to either. We appreciate there is a great deal to get to grips with when it comes to all things horticultural lighting, so as always please do get in touch if there’s anything that we can help with.

Brand Overview (A-Z)

We’ve used our extensive knowledge and experience of growing plants indoors to bring you the best grow lights out there from the leading brands on the market. All of the grow light products we stock are guaranteed to give you the best performance possible, and all have a great, solid reputation in the industry for being the best grow lights around.

AC Infinity is a premium brand known for its high-performance LED grow lights, ventilation systems, and smart environmental controls for indoor gardening. Their IONBOARD and IONGRID LED series feature high-efficiency Samsung LM301B diodes, delivering full-spectrum lighting with excellent PAR output for all plant growth stages. AC Infinity grow lights are designed with passive cooling, dimmable settings, and app-controlled automation, making them ideal for growers who want energy efficiency, low heat output, and precise control over their indoor environment. With a focus on innovation and smart technology, AC Infinity provides professional-grade solutions for hobbyists and commercial growers alike.

Adjusta-Watt, under the SOL Digital brand, is a well-regarded name in indoor grow lighting, offering adjustable digital ballasts and high-intensity discharge (HID) lighting solutions. Their dimmable ballasts allow growers to fine-tune wattage output, optimising efficiency and light intensity for different plant growth stages. SOL Digital also provides high-quality HPS, MH, and CMH bulbs, designed for maximum PAR output and longevity. Known for reliability, flexibility, and affordability, Adjusta-Watt/SOL Digital products are ideal for growers looking to balance powerful light output with energy efficiency while maintaining full control over their indoor grow environment.

Lumatek is a leading brand in the indoor grow lighting industry, known for producing high-quality, energy-efficient LED and HID lighting solutions. Designed for both hobbyist and commercial growers, Lumatek’s range includes full-spectrum LED grow lights, digital ballasts, and high-intensity discharge (HID) systems. Their LED fixtures offer high efficiency (often exceeding 2.7 µmol/J), excellent light distribution, and adjustable spectrums to support plants through all growth stages. With a reputation for durability, low heat output, and advanced control features, Lumatek is a trusted choice for growers looking to optimise plant health, yield, and energy savings.

LUMii is a trusted brand offering cost-effective and reliable indoor grow lighting solutions, including HID, CFL, and LED grow lights, digital ballasts, and reflectors. Designed for both beginners and experienced growers, LUMii products provide high PAR output, energy efficiency, and adjustable lighting options to support plants through all growth stages. Their dimmable ballasts and HPS/MH lamps allow growers to fine-tune light intensity, while their LED range offers full-spectrum efficiency. With a focus on affordability, ease of use, and solid performance, LUMii is an excellent choice for UK growers looking to maximise plant health without breaking the bank.

Maxibright has been busy manufacturing premium quality horticultural lighting since 1996. Through extensive industry research and a commitment to producing superior products, Maxibright has created an impressive range of grow lights and grow light accessories. All products are manufactured to CE and British Standards and all are RoHS compliant. Manufacturers of the successful Daylight and Varidrive LED ranges. Highly recommended.

Osram is one of the biggest light manufacturers in the world, supplying what they call “intelligent lighting.” They’ve been supplying lighting products to a range of industries for more than 100 years, starting back in 1908. Since then, Osram has consistently delivered reliable lighting that gets results. Highly recommended and they deserve to lay claim to the “intelligent lighting” title. Their Grolux range of dual spectrum bulbs is part of their highly respected Sylvania brand that is capable of providing a sufficient spectrum of light for both the vegetative and flowering/fruiting stages of the plant life cycle.

Philips needs no introduction as a renowned and superior-quality lighting manufacturer. As one of the leading lighting manufacturers in the world, Philips has created a full spectrum bulb known as the Philips Greenpower lamp. This bulb is very long-lasting and will still provide 95% light output after 5,000 hours of use, giving it a longer lifespan than most other bulbs on the market.

Sunmaster produces premium quality lamps specifically tailored for the horticultural industry. They are a top-quality manufacturer of the complete spectral range of lamps (Metal Halide, High-Pressure Sodium, Dual Spectrum, and 10K) that will accommodate all stages of the plant growth cycle.