A room with a high level of overall light levels can still look dark and still not function well. A single light source can illuminate the majority of the room, but not light the desk enough for reading, not illuminate the task light near a chair to read, nor light a picture to create a focal point. Sometimes, the problem is not the overall brightness of the room but is simply that we have overloaded the capabilities of a single light source by asking it to perform multiple functions. This is when you should learn to distinguish the difference of Ambient, Task, and Accent light.
Ambient lighting is simply the general level of light level within the room that helps you see your path and see the space as a whole. Ambient lighting is produced from a range of light fixtures like a suspended pendant, multiple downlights or ceiling lights, wall lights, indirect led lighting strips or light reflecting off a painted ceiling. Ambient light does not necessarily have the same light level all around the room. Instead, it should be used to provide an illuminating, background level without producing harsh direct glare and flattening of all surfaces. You can often provide a softer ambient level of light level by using broad beam angles, diffuse or shade covers and light reflecting from surfaces, rather than a single bright, direct and high-powered light source like an LED downlight in the ceiling.
A good task light will illuminate a particular activity. A desk light should illuminate the area of the desk you are working on, but not so you can read your shadow on the paper. A task light near your kitchen sink needs to illuminate that worktop, not the back of the cook. A reading light should illuminate the book, yet fall outside the direct line of vision of the reader. Where the task light is positioned, where its mounted, which way the beam is pointing and distance to the task light are all as important as its brightness (measured in lumens). A bright task light in the wrong place can actually produce a worse result in terms of task lighting.
A good accent light will attract focus and interest to a particular object of design in a room, like artwork, walls and their texture, shelves and plants or other interesting design features and details. It works through contrast, where the object is illuminated to a higher or lower level than its surroundings, which will bring attention to that area. You can often use narrow beam angles for this, but using narrow spotlights carelessly can create too much dark space and too much bright hot-spots on objects or walls. Accent light does not work if you are accenting every object equally. Instead, select one to two items you want to bring attention to, rather than having a room full of competing highlights.
To study how to layer these three types of light in the room you are planning, start by drawing a simple floor plan of the room, showing furniture, windows, working surfaces, and pathways of circulation and where focal points are. Then, make a copy of your floor plan, and create one for ambient light, task light and accent light separately. Add some notes next to each proposed light about what is its intended purpose. Your ceiling lights will provide a general area of ambient light, maybe a small table lamp at the reading corner will provide a small area for a focused reading light, or a track spotlight can direct a specific area like a wall. You should also ask yourself if this light is required or has a purpose or if it is just decorative and adds no purpose to the room or room layout.
Try out different lighting solutions to solve problems with a handheld movable lamp before investing in lighting. Try placing the lamp at different heights and angles and then evaluate the light within the room by standing or sitting within it. Consider if the light hits you in your eyes or you can use the space by blocking it with your body. See if there are reflective glares on the furniture, or other shiny surfaces. Take multiple photographs to see what the light looks from different vantage points or compare what the space looks like at dusk and during night time. Try altering only one factor, like beam direction or position and observe what is different. You will gain more insight on what has actually created that difference.
A successful lighting design plan can be created without all your lighting being switched on at any single time. You may have ambient light for circulation around the space, a focused light for the workspace for tasks and your accent light will be primarily switched on for the evening ambiance. The best test of a successful design plan is not maximum illumination, but rather being able to say what each light is for, what surface it lights up, and why it is located there.