Lighting output and colour
Does it mean what it says on the box? We explain the terminology for lighting.
Light output
We’ve probably all bought a low-energy lightbulb at some point and been disappointed with the result. It said “100 watt equivalent” on the packet, but when you got it home it just wasn’t that bright.
The problem is that “100 watt equivalent” doesn’t actually mean anything precise. The 100W figure is a measure of the electricity consumption of an old inefficient bulb, and is not a measure of brightness. This has allowed some manufacturers to make exaggerated claims, leading to confusion and disappointment. Unfortunately the same problem exists with LEDs. There are plenty of good LED products out there, but some companies are making extreme claims for very poor bulbs.
If you want to know how bright a light bulb really is you need a figure that measures its actual light output. Fortunately, bulb manufacturers now have to quote the light output on all new bulbs. Once all the old stock has been cleared from the shelves, every new bulb you see in the shops will have its light output in Lumens clearly printed on the packet. What does this mean?
Matching lumens to Watts for GLS bulbs
| Lumens | GLS equivalent | Where to use it |
| 1,200 to 1,300 | 100W | Usually the brightest bulbs in the house, single light fittings for lighting the whole room. |
| 650 to 700 | 60W | Wherever a less bright bulb will do, e.g. smaller rooms, rooms with more than one fitting. |
| 350 to 400 | 40W | Individual reading lamps, fittings that take more than one bulb. |
| 200 to 225 | 25W | Usually used to give ambient effect only, or to light cupboards etc. |
Matching lumens to Watts for halogen downlighters
When it comes to replacing halogen downlighters with LEDs, the numbers are slightly different. LEDs are naturally directional and don’t need reflectors to make them into spotlights. Also, halogens are often fitted in large numbers and may be giving off far more light than is actually needed. This means that an LED may be able to replace a halogen even if its output in Lumens is significantly lower.
| Lumens | Halogen equivalent | Where to use it |
| 300+ | 50W | If you currently have a few 50W halogens and you want to keep the same brightness. |
| 200+ | 35W | If you currently have 35W halogens, or lots of 50W and you could manage with less light output |
| 100+ | 20W | Usually for local lighting such as display cabinets, rather than general lighting. |
| less than 100 | - | Not usually useful. |
Colour
The sun gives out white light, and that is the sort of light we’re used to living in much of the time. But old fashioned light bulbs give out a much yellower light. When we’re indoors our eyes adapt to this and we think of this as “white”. If we then see a light source that is genuinely white, it actually looks blue by comparison. We call this a cold light, because we associate blue with cold and red or yellow with warm.
Most low energy bulbs - CFL or LED – are designed to mimic old fashioned bulbs to some extent, and are usually described as “warm white” or "soft white". This will usually be the preferred option for general household use. Bulbs that are sold as “cool white” or “pure white” are likely to look less attractive in the home, but may be appropriate for workplace lamps and anywhere where clear vision rather than ambience is the priority. "Daylight" bulbs are the whitest of all, and are usually only used by artists and others who need to match colours correctly.
Colour rendering
This is slightly different from colour. Two light bulbs can both give out white light, but certain colours will not show up well when illuminated by the first bulb, while they look fine under the second bulb. This means the first bulb has a lower colour rendering index (CRI).
Traditional bulbs have a CRI of 100. A good CFL will have a CRI of 80 or more, which is good enough for normal domestic use. Most LEDs have a CRI of 90 or more, so are usually fine. However, if you buy bulbs with a CRI of less than 80 there is a risk that the quality of light in your home will look a bit odd.
The CRI should be quoted on all bulb packaging somewhere. If you choose an Energy Saving Trust Recommended bulb you are guaranteed a CRI of at least 80.
