The elements of light
Light is science. The correct application of light is art. You really can't use light without fundamental understanding of both. To that end, I have outlined the key fundamentals of light - on the science & maths side - because without first principles, light just doesn't make sense.
Light is a physical medium. Sure, you can't see it until it hits something, but it has physical properties that are non-negotiable. Like gravity is non negotiable.
You can't "stop" light. It bounces around continuously until it has expended all of it's energy. The only thing that "stops" light, is a solid, impenetrable surface. This is vital when you're thinking about light in a room. You don't need light sources everywhere - you can use the room as one giant light fitting, and the sources can be positioned out of the way - providing the light can bounce all around and fill in the space.
Light is Rainbows. Rainbows are Light - diffracted. Don't believe me? Try on a pair of MINT glasses, and you will actually SEE light. It's different from every light source, depending on how that electric lighting source is made. Some have complete rainbows, some are less complete. Why does that matter? Because when light hits a surface, it reflects some of the colours - that's how we see colour. SO - if a colour is missing from the light source - then it follows that you will not be able to see that colour, as it can not be reflected from the surface.
When you realise that a "surface" can be anything from a tabletop, artistic masterpiece or even a face - then you can start to understand how important colour in light is. Without it - your beloved (or perhaps worse - you yourself!) might start looking green - or red - or grey under the lights in your home. Less than ideal. the solution is simple - buy lights with the most complete rainbow possible - which is listed as a "CRI" or Colour Rendering Index number on the packaging. look for 90+.
There is more than one type of colour when it comes to light. The content of the light is the rainbow (electromagnetic spectrum), but the LOOK of the light comes from something else entirely. The "Look of Light" is all about WARM or COOL light. Interestingly, though most of us don't realise it, daylight is really really BLUE. It becomes most obvious when you have daylight streaming through a window alongside WARM electric light - then you can see the difference. In our homes, WARM light is best - and that means 2700K - 3000K on the label, or WARM WHITE. The why of measuring light in this way, the how and the variations and discrepancies is a fascinating and detailed topic, which I won't bore you with here.
For a room to look and feel bright - you need a certain amount of light. That "number" changes, based on the colours of the room, the surfaces and the use of the room. A bedroom for example, doesn't usually need to be brightly lit - but a bathroom certainly does. So - how do you figure out if you have enough light? The number to look for when choosing lights is the "Lumen" output. This number tells you how much light is being made by that light fitting. So - for example, a wall light that makes 800 lumens, compared to a wall light that makes 2600 lumens is going to perform very differently in a room. If you have a small room, then maybe one or two of the 800 lumen wall lights is enough - providing you only want ambient light levels, but if you want LOTS of light, or you have a large room with high ceilings, you'll need to use the 2600 lumen light to put enough into the space to create that perception of brightness.
POWER. The amount of electricity consumed by a light fitting is critical when we're looking at having energy efficient homes and sustainable lifestyles. It also has a big impact on your bills each month. There is a direct correlation between the amount of power consumed and the amount of lumens created. Every light source is different, and with LED lighting, it can even vary across brands, but at the core of it, LED is a far more efficient source than any that have preceded it, and so, when used intelligently, can bring the perfect lighting into your home, for the lowest impost on the world and your hip pocket.
Critically - when comparing LED light fittings and light globes - compare on the lumens first. You can have a whole range of lights creating the same lumens, for varying wattages. The amount of light they make is far more important than the amount of energy they use.
As with anything - there are trade offs for the energy saving, but as the technology improves, the gaps in performance narrow, to the point where quality LED light can sometimes be better now than our old favourite perfect performer - Incandescent.