There are different methods to calculate how many recessed lights you need for a room, from calculations for general ambient light to building a lighting plan according to the activities of each area within a room.
For many years a quick method of calculating how many recessed lights are needed for general lighting was to multiply the room’s square footage by 1.5 or 1.7 for rooms needing brighter light, and then divide the result by the incandescent wattage of lights used, to estimate the number required and then find an LED equivalent.
So although this calculation still works, in the age of LED and the phasing out of incandescent lighting, lumens have become the standard for measuring brightness on packaging and specifications, fast rendering this calculation obsolete.
As an experienced lighting consultant for over 20 years, here are my two methods to determine how many recessed lights you need for your room in the age of LED lighting.
General lighting is the ambient light that fills the space as the main source of light and is best achieved from ceiling lights positioned in various lighting grid patterns.
With recessed lighting and dimmers, you can have full control over a room’s illumination. The recessed lights emit a conical downward light that requires a calculated spacing to evenly spread the light, taking into account the room’s size, ceiling height, and purpose of the space.
Before purchasing any fixtures you need to calculate your lighting needs by measuring the space and decide on a desired light level or illuminance.
Measure the room and create a floor plan shaped by the walls and include cupboards or high furniture like a wardrobe that needs some space between it and the recessed lighting. This plots out the available space in the ceiling for your lighting positions.
The intensity of the light depends on the lumen output of the product and the spacing distance between them. Using an approximate 500 lumen output LED recessed light, these are my general spacing receommendations:
The quantity of recessed lights needed is also determined by the height of your ceiling. Both taller and shorter ceilings usually require the same amount of lights but if the ceiling is higher than 9ft, you may need higher lumen outputs than 500 lm per light or reduce the spacings by 12″ between lights to include a greater quantity.
The final deciding factor for how many lights you need is how they fit within a recessed lighting layout.
General lighting works best within various grid patterned formats of equal spacings, so use your measured ceiling plan to judge the best shape to arrange them in, leaving an approximately 2 to 3 feet space between any wall or object.
Once you know how many lights you require, an online calculator can assist you in the specific spacings to suit your exact space.
Recessed lighting is a powerful tool to highlight specific areas and create a desirable atmosphere.
A considered lighting design always places recessed lights where light is needed rather than using a grid, but each have their merits and both techniques can be combined in the same room.
Use layered lighting design techniques such as wall washing, create focal points, create accent light and avoid dark corners, to build a combination of groupings.
This method takes into consideration specific light levels that you may wish to achieve for certain activities within a room.
Where are the activities that require task light? Where do you need ambient light, what areas are best left unlit? Build a lighting plan using recessed lights to assist in the layering of light.
Draft a room plan including the furniture and built in furniture, and add the chosen groups of lights, building up a reflected ceiling plan that is organically designed by where the light is needed.
For example, have a group spaced at 32″ apart over a kitchen island and dining table for task lighting, alongside a small grid of 46″ apart for general light.
The lighting ceiling plan example below drawn on CAD software, shows a project where we used grouped and individual recessed lights over the task areas and for general light, resulting in 9 or 10 lights in a 8.5′ x 10.5′ ensuite bathroom.
Use each grouping of lights to total an approximate lumen level.
For example, over a kitchen island the task lighting achieved by 3 qty 500lm lights at a spacing of 32″, delivers 1500lm. You can then choose another type of recessed light to deliver the required illumination, for example a single 12″ diameter LED recessed ceiling light, using 1 instead of 3 qty.
This stage can be skipped for a beginner, but a lighting designer would break down the activities that will occur in each area of your room and assign an appropriate lux level for each activity and how many lumens would be required to achieve that brightness.
For example, a lower lux level of 200 can be used for general living areas and higher levels like 500 could be used for task lighting.
Consider creating pools of light instead of using too many lights in one room to improve lighting efficiency and create an appealing contrast between lit and unlit areas.
The placement of each light is further determined by potentials obstacles hidden within a ceiling, like floor joists, pipework or other services. Survey your ceiling, add these to the plan and space the lights where you know they can be recessed in the ceiling.
A hybrid method combines the grid layout of lights with the total lumens needed for the whole room averaged out to determine how many recessed lights you need by their combined lumen output.
A products specification contributes to the number of lights required.
The number of recessed lights you need is also influenced by the type of fixture that will be delivering the light. Not all recessed lights deliver the 500lm average used in our spacing recommendations.
Use the total lumen output calculation for each area to choose alternatives that can deliver the same illuminance.
Select the recessed ceiling lights that are appropriate for the size of your space. Wide areas can benefit from large wide beamed lights whilst domestic and hospitality applications work best with 3″ diameter can lights.
The beam angle is how wide the light spreads from the light, affecting how far apart you should space the lights on the ceiling.
For example, this diagram demonstrates the spread of light from an 80 degree beam width with lights spaced at 1200mm (4ft) apart, showing a beam overlap at 700mm (27.5″) from the ceiling but if you want the overlap to be higher and create more intense light, spaced closer at 850mm (33″) apart the overlap begins higher at 500mm (20″) from the ceiling.
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