In this section we will try to cover the following five areas where most of the questions arise.
1. What are Lumens ?
2. What does Kelvins mean ?
3. why have different beam angles ?
4. What are Reflectance values ?
5. Why use LED lamps ?
Each of the above first 4 areas have a baring on each other and can determine which lamp source is best for you. No matter what type of lamp you choose every one will have a kelvin rating, a lumen output, a wattage and in some cases a beam angle. Not every lamp has a beam angle because the reflector within the light fitting can control the light angle emanating from it.
This will include:-
Metal halide lamps
Low voltage lamps
Mains halogen lamps
LED lamp all varieties
How much light do you need
What are Lumens ?
What are kelvins ?
The colour of a lamp is defined as a measurement called kelvins. A standard GLS light bulb in your house would be 2,700 kelvins which is in the warm colour spectrum and a lamp with 6,000 kelvins would be at the very cold white spectrum. Getting the right colour temperature of a lamp does matter as the warm colour wavelength helps to soften skin tones and gives a warm soft relaxed feel and at the other end of the scale a 4,000 to 6,000 kelvin lamp colour would be used in offices or in fast food restaurants to make you feel less comfortable and relaxed and more alert. There’s nothing that can sour your opinion of a compact fluorescent or LED lamp like buying a 4000K or 5000K bulb when you meant to buy a 2700K bulb, or vice-versa. When you buy a new, energy efficient bulb, keep your application and colour scheme in mind and make sure to buy the bulb with the correct colour temperature to match the environment you are putting it in to. A brighter whiter lamp around 6,000 kelvins will seem brighter to the naked eye than a warm colour lamp so you could in theory have less lumens but still have the same amount of light. FIG 1 shows a kelvin colour chart to explain further how it works.
Why have beam angles ?
It may seem an obvious thing but is generally something that is overlooked by many clients. Beam angles have an effect on the intensity of light reaching a given area and can change the amount of light ( LUX ) falling on that area. For example you can have LED lamps both producing 450 lumens and both in a cool white 6,500 kelvins, but one has a 90 degree beam angle and the other a 38 degree beam angle. The distance to the object is the same but the 90 degree lamp only produces half the light on the given area compared to the 38 degree lamp. That's because the light is thrown in a much wider area and by the time it reaches it's given destination the concentration of light is much softer. If an object is long and tall like a silver birch tree you will need a narrow beam angle to punch light right to the top, where as if the tree was a wide oak you would need a wide beam angle to cover the whole tree but you would also need to increase the lamp lumen's to get the same amount of light. Some lamps like low voltage LED MR16 and mains LED GU10 lamps have the beam angle built into the lamp so it is easy to make an informed choice, however bollard lights tend to have an internal reflector or series of louvres to throw the light in all directions and therefore the lamp will not need a built in beam angle. Security flood lights are another prime example of the light fitting controlling the beam angle rather than the lamp housed in the fitting.
What are reflectance values ?
Another area that is generally overlooked and should always be taken into account when deciding on what lamp is required. In basic terms the whiter an object the higher the reflectance values will be. A good example would be standing at an entrance of a very dark cave and shining a light right down the centre, what would you see ? the answer would be not a lot because the light has nothing to reflect against, so light is invisible until it hits a reflective surface. So now if you shine that same light to the side onto the cave wall some of it will reflect back into the main area and you would see more. If you wanted to increase the light even further without increasing lamp lumens you could simply paint the walls white and hey presto your lamp seems 4 times brighter. So in the real world you want to illuminate your steps which are slate grey you would need a lamp that produces 3 to 4 times more lumens than a lamp that needs to illuminate the same steps made of sandstone.
Why use LED lamps ?
The straight forward answer to why you should use LED lamps is their massive energy saving over traditional style halogen lamps. But there are a few other reasons to consider switching to LED lamps. They are cool to touch so this makes them safe around children and pets, they last much longer than most lamps on the market, they can be retrofitted into many types of light fittings, they can be used with a photocell or PIR sensor, some lamps can also be dimmable but take care to ensure they have a compatible dimmer or they may not work. However there does become a point when the LED lamp just can not compete on lumen output and price compared to Metal Halide lamps. A 70w Metal Halide lamp can produce 7,500 lumens and can last up to 15,000 hours, to buy an LED light fitting that produces this amount of light is currently expensive, so using LED lamps in smaller applications and some security flood lighting is fine and they will in time get better and cheaper.