Ten years ago the answer was easy: HPS, every time. Today most of the lights leaving our shop are LED, but HPS still has a place. This guide gives you the honest comparison, with real UK electricity numbers, so you can decide which suits your grow and your budget.
The short version
- Buy LED if you plan to grow for more than a year, your room runs warm, or you want the lowest electricity bill.
- Buy HPS if your upfront budget is tight, your room is cold, or you already own the ballast and reflector and just need a lamp.
Everything below explains why.
Upfront cost
HPS wins on day one. A 600W HPS kit with a digital ballast, reflector and lamp costs roughly £90-£150. A quality 600-720W LED bar light that covers the same 1.2 x 1.2m area costs £400-£700. Cheaper LEDs exist, but a £150 LED panel will not match a 600W HPS over a 1.2m tent, whatever the box says.
The gap closes over time, which brings us to electricity.
Running cost: a worked UK example
Electricity is the biggest hidden cost of indoor growing. Let us compare a 600W HPS and a 720W LED over a 1.2 x 1.2m tent.
Assumptions (adjust these for your own tariff and schedule):
- Electricity at 27p per kWh. Check your bill, as tariffs change.
- Vegetative stage: lights on 18 hours a day for 4 weeks.
- Flowering or fruiting stage: lights on 12 hours a day for 9 weeks.
600W HPS. The lamp draws 600W but a digital ballast adds around 5-10%, so call it 650W. Many growers also need a bigger extractor fan to cope with the heat, which adds roughly 40-60W of fan.
- Veg: 0.65kW x 18h x 28 days = 328 kWh
- Flower: 0.65kW x 12h x 63 days = 491 kWh
- Total: around 820 kWh, or about £221 per grow cycle for the light alone.
720W LED. Most 720W bar lights are dimmable, so growers run them at 50-60% in veg and full power in flower. Lower heat means a smaller fan running slower.
- Veg at 400W: 0.4kW x 18h x 28 days = 202 kWh
- Flower at 720W: 0.72kW x 12h x 63 days = 544 kWh
- Total: around 746 kWh, or about £201 per cycle.
That looks close, and it is, because a 720W LED is a more powerful light than a 600W HPS. If you ran the LED at 600W for a like-for-like output you would use closer to 620 kWh, around £167. The real saving comes when you add the extraction and the yield.
Over a year (three grow cycles) the LED saves roughly £100-£160 in electricity, plus fan running costs, plus the HPS lamp replacement below. Over three years the LED has paid back its higher purchase price, and from then on it is cheaper every month.
Heat
This is where LED wins hands down, and for a lot of UK growers it is the deciding factor.
An HPS lamp converts most of its energy into heat and infrared. In a 1.2m tent a 600W HPS will push the temperature up 8-12°C above the room unless you have good extraction. In a spare bedroom in summer, that means a 30°C+ tent and stressed plants.
A 720W LED still produces heat (every watt you put in has to go somewhere), but it comes off the heatsinks as warm air rather than radiant heat beating down on the leaves. Typical rise is 4-6°C above the room. You can hang the light closer to the canopy and run a smaller, quieter fan.
The flip side: in a cold garage or outbuilding in winter, HPS heat is free heating. Some growers switch to HPS for the winter cycle and LED for summer. If you are only buying one light, that is an argument for a modest grow tent heater on a thermostat alongside an LED.
Light quality and results
Modern full-spectrum LEDs from brands like Maxibright, Omega and Lumii produce a spectrum that suits plants from seedling to harvest. HPS is heavy in the orange and red end, which is excellent for flowering and fruiting but weaker for compact vegetative growth. Many HPS growers use a separate metal halide or dual spectrum lamp for veg.
In terms of output, the useful comparison is micromoles per joule (µmol/J), which tells you how much usable light you get per unit of electricity.
- 600W HPS with a good reflector: around 1.7 µmol/J
- Quality 720W LED bar light: 2.7-3.0 µmol/J
That is 50-70% more light per unit of electricity. In practice, growers switching from a 600W HPS to a 720W LED in the same tent usually see similar or better results with less heat, provided they adjust their feeding. Plants under LED often transpire less and need slightly less water and sometimes more calcium and magnesium.
Lamp life and maintenance
An HPS lamp loses output steadily and most growers replace it every three or four cycles, at £20-£40 a time. Ballasts last for years but do fail. Reflectors need cleaning.
A quality LED is rated for 50,000 hours or more, which is well over ten years of growing. There is nothing to replace. The risk is driver failure, so buy from a brand with a proper UK warranty (three to five years is normal) rather than an unbranded import.
Dimming and control
Most LED bar lights have a dimmer and many take a 0-10V controller, so you can run one light from seedling to harvest, ramp it up gradually and even link several lights together. Digital HPS ballasts dim too (usually 250W, 400W, 600W and a boost setting) but the lamp spectrum shifts when you dim it, and you cannot dim below about 50%.
Which should you buy?
| LED | HPS | |
|---|---|---|
| Upfront price | Higher (£400-£700 for 1.2m tent) | Lower (£90-£150) |
| Electricity | Lower | Higher |
| Heat | Low to moderate | High |
| Lamp replacement | None | Every 3-4 cycles |
| Spectrum | Full, veg to harvest | Flower-focused |
| Lifespan | 50,000h+ | Lamp 5,000-10,000h |
| Best for | Warm rooms, long-term growers, low bills | Tight budgets, cold rooms, existing kit |
If you are starting from scratch and can afford it, buy a good LED. If you are on a tight budget, a 600W HPS kit is still a proven, reliable way to grow, and the money you save can go on a better fan and filter. You can always upgrade to LED later and keep the HPS as a winter light.
Talk it through
Every room is different. Tell us your tent size, what your room temperature is like and how much you want to spend, and we will point you at the right light. Call 0121 553 7872, message us on WhatsApp, or come into the shop in West Bromwich. We stock LED grow lights, HPS grow lights and kits and replacement lamps, and we price match.