Halve your ceiling height for the gap between downlights, then halve that again for the distance to the wall. On a 2.4m ceiling that is 1.2m apart and 0.6m in from each wall, which puts twelve fittings on the grid in a 4m x 5m room. That sum is our starting point rather than a standard, and most rooms want fewer once each fitting has to justify itself.
Before you count them, make five decisions, in this order: fire-rated or not, sealed or not, GU10 or integrated LED, what your ceiling can take, and which lamp goes in it. Get the first two wrong and you will be swapping fittings. One customer bought a pack of our Astro Trimless Round Fixed, found there was no glass cover and returned them. Another bought a surface bezel, which is a trim ring, believing it was a discounted light. Neither was being careless. Downlights come with their own vocabulary, so here it is, with the consequence attached to each word.
Decision one: does it need to be fire-rated?
If there is a room above the ceiling you are cutting into, we would say yes. If there is a loft above it, we would still say yes, and that second part is our recommendation rather than the regulation.
A downlight is a hole in a ceiling. Where that ceiling belongs to a floor, the floor has a job to do in a fire. In England, Approved Document B sets the minimum fire resistance for it: 30 minutes for a floor in a typical two-storey house, and typically 60 minutes for a floor between flats. A fire-rated downlight is the simple way through, because its maker rates it to hold that figure in a named type of ceiling.
The guidance is more careful than most sales talk, ours included. A 2005 article from the body behind the wiring regulations reports tests in which downlights made little significant difference to plasterboard ceilings on conventional rectangular joists, up to 30 minutes. It treats flats differently, because the floor there is a fire compartment and its resistance has to be restored, and it recommends asking local building control. So do we, if you are unsure. Those tests say nothing about I-joists or metal web joists, which is why a good fire rating names the joist.
We would fit fire-rated under any room or loft regardless, because the decision is hard to undo once the ceiling is finished and it may cost nothing extra. The Collingwood H2 Lite IP65 in Matt White at 3000K (£13.75, checked 2nd November 2026) is fire-rated to 30, 60 and 90 minutes in solid timber and 30 minutes in an I-joist or metal web ceiling, with the LED built in. The Astro Minima Round Fixed (£11.30, checked 2nd November 2026) is not fire-rated and needs a lamp: add an Astro 3.7W 3000K (£8.76, checked 2nd November 2026) and it comes to £20.06. The fire-rated fitting is the cheaper by £6.31. At 4000K the same H2 Lite (£7.90, checked 2nd November 2026) is cheaper still, and the colour question is in decision five.
One customer's verdict on the 4000K, from 27th October 2025: 'I have now fitted and they are all working perfectly.' That was Wade M., who bought four.
A ceiling with nothing above it, such as a flat-roof extension? The floor rule is not in play, so the fire rating is your choice, and your electrician or building control can confirm it for your house. The insulation point in decision four still applies.
Decision two: does it need to be sealed?
An IP65 downlight keeps water and dust out. An IP20 one does not, and that is how one order came back to us. In the customer's words: 'However I purchased these downlights and they don't have glass covers so had to be returned.' That was Nathalie T., on 20th March 2026.
She had bought the Astro Trimless Round Fixed (£23.39, checked 2nd November 2026), an IP20 fitting for dry ceilings. The sealed Trimless is the Astro Trimless Slimline Round Fixed Bathroom (£46.69, checked 2nd November 2026): IP65, fire-rated, rated for bathroom zones 1 and 2, and made to go into a new ceiling. For a ceiling that is already up, the Astro Minima Slimline Round IP65 Fire Rated (£21.70, checked 2nd November 2026) comes from a different range, and is also sealed and fire-rated. Here is where each rating belongs.
| Where the downlight goes | What it needs | Why |
|---|---|---|
| Over a bath or in a shower enclosure | At least IPX4; we would choose IP65 | The wiring regulations ask for IPX4 in zones 1 and 2, and IPX5 where water jets are used for cleaning. IP65 is our recommendation, not the regulation. |
| Elsewhere in a bathroom | We would still choose IP65 | Outside the zones no special fitting is required, though it must suit the conditions. Steam does not respect a zone line, and on the Minima the sealed IP65 version is only £3.20 more. |
| A kitchen ceiling | IP20 is fine | Away from the hob extract, a kitchen ceiling is a dry ceiling. |
| A living room, bedroom, hall or landing | IP20 | Nothing is going to splash it. |
| A soffit, porch or covered outdoor ceiling | IP65 and made for outdoors | Wind-driven rain gets under a soffit. An IP65 rating alone is not enough: Collingwood says the H2 Lite is not for exterior use and points to the H2 Pro Extreme, such as this one in black (£26.32, checked 2nd November 2026). |
For bathrooms, stop here. How many downlights a bathroom needs covers the count and the mirror decision, the best bathroom downlights covers the fittings, and IP65 versus IP44 covers what the two ratings actually mean.
Decision three: GU10 or integrated LED?
GU10 means the fitting is an empty housing and you buy a lamp to put in it. Integrated means the LED is built in, and when it dies the fitting dies with it. On the H2 Lite that is rated at 70,000 hours with a ten year warranty. The Astro GU10 fittings in this guide carry three years, and the lamp is yours to replace.
GU10 buys you a change of mind. Swap 3000K for 2700K, or a failed lamp for £5.95, without calling an electrician. Integrated costs less to buy when you are fitting a lot of them: twelve H2 Lites at 3000K come to £165.00, and twelve Minimas with lamps come to £240.72. That is £75.72 for the right to change your mind.
Our view: in a kitchen, or anywhere you are fitting ten or more, go integrated and buy the colour you want once. In a living room or a bedroom, where you will change your mind about the light long before the LED fails, buy GU10 and keep the option.
GU10 is also where you get to aim the light. The Astro Minima Round Adjustable (£11.81, checked 2nd November 2026) tilts 40 degrees and rotates 360, which is useful for pulling a beam off a wall or onto a worktop, but it is not fire-rated, so it belongs in a ceiling with nothing above it. The Minima Slimline Round Adjustable (£22.22, checked 2nd November 2026) tilts 30 degrees and is fire-rated, which is the pairing we would reach for under a bedroom. If you do not need to aim it, the Astro Taro Round (£19.45, checked 2nd November 2026) is a fixed GU10 fitting rated to 90 minutes to BS 476 Part 21.
Decision four: what the ceiling can take
Three things decide this, and none of them is on the product photograph: the cut-out, the depth above the plasterboard, and whether insulation can sit on the fitting. These are the makers' own figures, from their spec sheets and our listings.
| Fitting | Cut-out | Depth it needs | Insulation over it? |
|---|---|---|---|
| Collingwood H2 Lite IP65 | 64 to 72mm | 46mm body, with a separate driver 123mm long | Yes, rolled and blown |
| Astro Minima Round Fixed | 76mm | 150mm | No |
| Astro Minima Round Adjustable | 76mm | 150mm | No |
| Astro Trimless Round Fixed | 79mm | 150mm | No |
| Astro Pinhole Slimline Round Adjustable | 83mm | 150mm | No |
| Astro Minima Slimline Round IP65 | 86mm | 150mm | No |
| Astro Taro Round Fire-Rated | 86mm | 172mm | No |
| Astro Blanco Round Adjustable | 152mm | 150mm | No |
The cut-out is the hole. Get it wrong and you are filling and painting. That goes double if you are replacing old fittings, because the new rim has to cover the old hole, so measure it before you order. One customer put it well on the Pinhole: 'Needs clean cut holes for a nice fit as there is only a small distance from the inner body to the outer edge of the ring.' That was Aaron T., on 25th September 2025.
The depth is the space above the plasterboard, and the Astro fittings above need about three times the H2 Lite's body depth. Check it from the loft or ask your electrician to, particularly in a ceiling with a joist or a pipe close above it. Better to find out now than while holding the fitting.
Insulation is the one to read twice under a loft. Every Astro fitting in that table is marked as not suitable for covering with thermal insulation, and IET guidance says insulation must not surround or touch a downlight of that kind in a ceiling with a loft above. Collingwood rates the H2 Lite as coverable with rolled and blown insulation, which is why it would be our first call under a loft. If you want GU10 there, Astro's insulation guard (£6.21, checked 2nd November 2026) is made to keep loft insulation off the fitting. Its instructions draw it around 62mm and 86mm cut-outs, so check it against yours.
There are two ways to lose the rim altogether. Astro's Trimless range goes into a new ceiling before it is finished. The Astro Blanco Round Adjustable (£43.69, checked 2nd November 2026) goes into a ceiling that is already plastered: the gap is filled, rubbed down and painted. It is nearly four times the price of a Minima and needs twice the hole. The Blanco Round Fixed (£27.70, checked 2nd November 2026) is the cheaper route if you do not need to tilt it, with a 133mm cut-out. If you are decorating anyway, we think the money is well spent. If you are not, it is a lot to pay to get rid of a rim you could have painted.
Decision five: which lamp, and the wattage ceiling nobody reads
If you went GU10, the fitting is half the purchase. The lamp decides the colour, the output and whether it dims, so read the maximum wattage on the fitting first. The Minima family alone runs from 50W on the Minima Round Fixed, to a 6W maximum LED on the Minima Slimline, to a 4W maximum LED on the Minima Mini, which takes a smaller 35mm lamp altogether. A 50W halogen left over from the old ceiling does not go in a fitting rated for 6W.
The three standard 50mm lamps below all sit at 5W or under, so they clear the 6W and 50W limits. All four lamps throw a 36 degree beam.
| Lamp | Output | Colour | Dims? | Price |
|---|---|---|---|---|
| Astro 3.7W 3000K | 350lm | 3000K | Yes | £8.76 |
| GU10 4.2W Warm White | 450lm | 2700K | No | £5.95 |
| GU10 5W Natural White | 400lm | 4000K | No | £5.95 |
| Astro 35mm 3W 2700K, for 35mm fittings such as the Minima Mini only | 230lm | 2700K | Yes | £8.09 |
Prices checked 2nd November 2026. For the same £5.95 the 4.2W lamp gives 450 lumens and the 5W gives 400, which is why you buy on lumens rather than watts. Do the same when replacing halogen. Astro rates its 350 lumen lamp as the match for a 50W halogen, and eight of them draw about 30W against the 400W of the old set. If a room looks dimmer after a swap, compare the lumens and the beam before you blame the LED.
On beam angle. The sum is plain geometry. On a 2.4m ceiling a 36 degree beam makes a pool about 1.6m across on the floor and about 1m across on a worktop 900mm high. So at a 1.2m gap the pools overlap on the floor and stop short of each other on the worktop. The H2 Lite's 55 degree beam makes about 2.5m and 1.6m, so it overlaps at both heights. In a narrow hall or on a low ceiling, a narrow beam is how you end up with nine circles on your carpet. A wider beam, or wall lights, will serve you better.
On colour. Our view is 3000K in a kitchen, 2700K where you relax, and 4000K only over a work surface where you need to see detail. Is 3000K or 4000K better for a kitchen? 3000K, and it is not close. On the H2 Lite that costs £70.20 more across twelve fittings, and we would still pay it. In a living room on a dimmer, the 3.7W 3000K is the lamp in that table to use. Warm white versus cool white argues the colour question at greater length.
Now the number: how many downlights does a room need?
This is our rule of thumb rather than a standard, so check the result against the room. Four steps:
- Halve the ceiling height. That is the gap between fittings: 1.2m on a 2.4m ceiling.
- Divide each wall's length by that gap, and round to the nearest whole number. That is how many fittings run along it.
- Multiply the two numbers together. That is your grid.
- Space them evenly along each wall, with half the gap at each end. That keeps the light reaching the edges of the room.
Take a 3m x 4m kitchen on a 2.4m ceiling. Divide 3 by 1.2 and you get 2.5, so two or three. Divide 4 by 1.2 and you get 3.3, so three. That gives six or nine. With six, the three along the 4m wall sit 1.33m apart and 0.67m off the wall, and the two along the 3m wall sit 1.5m apart and 0.75m off it. That is a little wider than 1.2m, so check it against the worktops before you settle on six rather than nine.
The half-gap to the wall is the same ratio the lighting maker ERCO recommends. ERCO allows a wider gap between fittings than we do, so ours errs towards more fittings, which is one more reason to take some out. A taller ceiling widens the gap: 1.35m on a 2.7m ceiling and 1.5m on 3m, where the same 4m x 5m room drops from twelve to nine. If you want it per square metre, it is roughly two fittings for every three square metres on a 2.4m ceiling, but use the walls, because a long thin room and a square one of the same area want different grids.
| Room on a 2.4m ceiling | Example size | The grid says | What we would actually do |
|---|---|---|---|
| Cloakroom or small utility | 1.5m x 2m | Two | Two, and nothing else needed. |
| Hall | 1.2m x 5m | Four | Fewer, and add wall lights. Downlights are the tempting answer in a narrow hall and the wrong one. |
| Kitchen | 3m x 4m | Six to nine | That many, on at least two switches, over the front edge of the worktops rather than the walkway. |
| Larger kitchen | 4m x 5m | Twelve | Twelve is fine here, on at least two switches. |
| Living room | 4m x 5m | Twelve | Six on a dimmer, doing background work, with lamps and a pendant doing the real job. |
| Bedroom | 3m x 3.5m | Six to nine | Four, dimmed hard, or none at all. |
| Large lounge | 5m x 6m | Twenty | About ten, split into zones on two dimmers. |
The grid and the right-hand column disagree on purpose, and the reason is light. Our working figure for a living room is 100 to 150 lumens per square metre from the ceiling, which is 2,000 to 3,000 lumens in a 4m x 5m room. Twelve H2 Lites give 5,520, almost twice the top of that range. Six 350 lumen lamps give 2,100, which sits inside it. The same sums put four such lamps at 1,400 in the 3m x 3.5m bedroom, against 1,050 to 1,575, and ten at 3,500 in the 5m x 6m lounge, against 3,000 to 4,500. A kitchen earns its extra fittings because you work under them.
A ceiling laid out like a car park lights the floor beautifully and everything you care about badly. So work out what the grid says, then ask what each fitting is for. Any downlight that cannot answer comes out of the plan, and the money goes on a dimmer instead. Collingwood says the H2 Lite works with leading and trailing edge dimmers, and our dimming guide covers which dimmer to choose. For a room with more than one job, our open-plan kitchen diner guide plans it by zone.
What your electrician needs to know
We sell the parts. We do not wire them. In England, Part P of the Building Regulations makes a new circuit, a new consumer unit and additions or alterations around a bath or shower notifiable. Other electrical work still has to meet the regulations. Wales has its own Approved Document P, and Scotland and Northern Ireland run separate systems. The wiring is your electrician's call, not ours.
What they will want from you:
- The quantity, and the cut-out diameter.
- The depth above the plasterboard, and what the joists are.
- Whether the fittings are fire-rated, and whether there is insulation above them.
- Whether any are going into a bathroom zone.
- Whether the circuit is going on a dimmer.
How many downlights can share one circuit and one dimmer is a question about load and cable, which is theirs to answer with the actual numbers in front of them. None of the fittings in this guide needs a separate driver bought for it: the GU10 ones run straight from the mains and the H2 Lite has its own. Astro does sell some that do, and they say DRIVER REQUIRED in the title. If your old downlights run on 12V with a transformer, ask your electrician to deal with that before you order mains lamps.
The short version
- Fire-rate anything with a room or a loft above it. That is our view, and at £13.75 complete against £20.06 for a plain fitting and lamp, it need not cost more.
- IP65 for bathrooms and soffits, with outdoor-rated fittings outside. IP20 is fine on a dry ceiling.
- GU10 where you will change your mind, integrated where you are fitting ten or more.
- Check the cut-out, the depth and the insulation before you order, not after.
- Read the fitting's maximum wattage. The Minima family alone runs from 4W to 50W.
- Halve the ceiling height for the gap, halve it again for the wall, then take fittings out until every one has a job.
Frequently asked questions
How many downlights do I need in a room?
Halve the ceiling height for the gap, divide each wall by that gap, and multiply the two. On a 2.4m ceiling a 3m x 4m kitchen comes out at six to nine, and a 4m x 5m room at twelve. Then take some out. A living room that size is far better served by six on a dimmer, with lamps doing the rest.
How far apart should downlights be, and how far from the wall?
Half the ceiling height between fittings, and half of that to the wall. That is 1.2m and 0.6m on a 2.4m ceiling, and 1.5m and 0.75m on a 3m ceiling. It is our starting point, not a standard. Worktops and furniture beat it every time, because the light should land where you use it.
Do downlights have to be fire-rated?
The rule applies to the ceiling rather than the light. In England, Approved Document B sets a minimum fire resistance for floors, usually 30 minutes in a two-storey house and typically 60 between flats. A fire-rated downlight is the simple way to keep it. We would use one under any room or loft, and ask building control if you are unsure.
What is the difference between a downlight and a spotlight?
A downlight is recessed into the ceiling and aims down. A spotlight sits below the ceiling on a plate, bar or track and can be aimed anywhere. If your ceiling has no void, or you are renting, surface fittings or track need no holes, and lighting a room you cannot rewire has more.
Can I put a downlight in a bathroom?
Yes, with the right rating. Over a bath or inside a shower enclosure the wiring regulations ask for at least IPX4 in zones 1 and 2. We would choose IP65, which is our recommendation rather than the regulation. The Astro Minima Slimline Round IP65 Fire Rated is £21.70, checked 2nd November 2026. Any new circuit or alteration there is notifiable in England.
Which GU10 bulb goes in a downlight?
Check the fitting's maximum wattage first, because it runs from 4W to 50W across the Minima family alone. Then choose by colour and dimming. For a standard 50mm fitting, the Astro 3.7W 3000K dims and gives 350 lumens, and the 4.2W 2700K gives 450 lumens but does not dim. The 35mm lamp is only for 35mm fittings.
Are integrated LED downlights better than GU10?
They are better if you are fitting ten or more and know the colour you want: twelve H2 Lites are £75.72 less than twelve Minimas with lamps. GU10 wins on flexibility, because you can change the colour or replace a failed lamp for £5.95 without an electrician. So fit integrated in the kitchen and GU10 where you may change your mind.
What LED replaces a 50W halogen downlight?
Astro rates its 3.7W 3000K lamp, at 350 lumens, as the match for a 50W halogen, so eight of them draw about 30W against 400W. Compare lumens and beam, because a narrower beam can make a room look darker. That lamp suits mains GU10 fittings. If yours run on 12V with a transformer, ask your electrician first.
Do I need an electrician to fit downlights?
We would always use one, and we never give wiring instructions. In England, a new circuit, a new consumer unit or additions and alterations around a bath or shower are notifiable under Part P. Wales has its own version, and Scotland and Northern Ireland run separate systems. An electrician will also check the joists, the void and the load.
