8 things to check when buying your next light bulb

It's probably you who buys and changes the light bulbs... But I can't resist a few lame light-bulb jokes:

How many Google engineers does it take to change a light bulb?

  • 20. One to hold the bulb, 19 to turn the room around.

How many Apple employees does it take to screw in a light bulb?

  • 10. One to screw it in, two to design the icon, four to design the T-shirts, and three to come up with the code name for the project.

How many Microsoft engineers does it take to change a light bulb?

  • 0. They merely change the standard to darkness and then upgrade the customers.

Jokes aside, buying a replacement light bulb (such as an LED downlight) is often an unnecessarily complicated experience. In particular, choosing an energy efficient option and getting poor results is all too common.

In an effort to streamline this process, I've outlined the top 8 considerations when choosing replacement lights at home or work.

1. Fixture and lamp type

Simply rocking up to the store with the old globe in-hand is not the best option. Sure, you will probably come home with a working replacement... but are there more efficient options available that would also work, and save you money in the process? The easiest way to check this is to find the lamp-type code on the box.

This will allow you to seek out more efficient lighting technologies (see next point) which come with the same fitting. For example, a standard Edison Screw fitting is labeled E27 or ES, the compact ones are E14 or SES, regular bayonet's are B22 or BC, and so on.

See also: our related blog post on light bulb codes and what they mean.

2. Lighting technology

Once you know the fixture type you can aim to upgrade to a more efficient technology. In summary, from least efficient to most efficient, we have:

  • Incandescent (generally the least efficient)
  • Halogen
  • IRC Halogen
  • Compact Fluorescent
  • T8 Fluorescent
  • T5 Fluorescent
  • LED (we sell a range of Philips LEDs)
  • Metal Halide
  • High and Low Pressure Sodium (generally the most efficient)
Note: Sodium lamps are very efficient but are generally only practical for very niche applications, such as street lighting. Metal halide lamps are also only used in specific higher-wattage applications.

    3. Fixture wattage vs. Lamp wattage vs. Equivalent wattage

    If only things could be simple and a 15 watt light bulb means 15 watts! Unfortunately, this is not always the case. For starters, everyone who sells a compact fluorescent light bulb feels compelled to list an "equivalent" incandescent wattage. So, you will often see things like 15 watts = 60 watts. LED sellers are even worse: in the vast majority of cases, they give an equivalent wattage which is simply not true.

    From an energy consumption perspective, '15 watts' is of course the important part. But you also need to consider what fixture you are putting the lamp in. For example:

    • A 36 watt T8 fluorescent light bulb actually uses about 45 watts once you add the consumption of the fixture. See our new Philips LED Tube.
    • A 50 watt MR16 halogen down-light actually uses close to 65 watts when you include the transformer. See our new 7 Watt MR16 LED and low-power LED Driver.

    To avoid further confusion, it is worth noting that a regular 15 watt compact fluorescent light bulb does use 15 watts (because it is has no additional control gear in the fixture).

    4. Colour temperature

    Did you manage to score a box of free light bulbs from your energy company a few years ago? The 'free light bulb' programs were designed to reduce consumption and greenhouse emissions in the cheapest way possible.

    One of the biggest criticisms of the energy saver lights was that they "looked ugly." This was more a result of the market being flooded with lamps with a high Correlated Colour Temperature (CCT), than an actual problem with the technology.

    Lighting Colour Temperature Examples 

    In summary, if you want a light to mimic the warm glow of an incandescent or halogen globe, choose warm white. It will be specified on the box in those words or with the numbers below:

    • Warm white is equivalent to about 2,700 K (it's 'colour temperature' in degrees Kelvin)
    • Cool white or 'day light' globes are generally above 4,000 K (think regular office lighting)

    5. Lumen output

    If you are worried about how bright a light bulb will be, check its lumen output. The total lumen output is the only real way to understand how much light a lamp will put out. In technical speak:

    Lumen - The SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.

    6. Lamp lifetime

    This one is really important when looking at the cost of light bulbs. The $2 lamp may seem cheap compared to the $5 option, but not if it's lifetime is a quarter of the other.

    Lamp lifetimes vary greatly, so check the box before you buy. They vary anywhere from a  few hundred hours (specialised lamps used in theatre, for example) through to 50,000 hours for well made LEDs.

    If a company claims very long lamp lifetimes, it's worth checking if they offer a warranty. 50,000 hours is long time - almost 6 years (and who leaves their lights on 24/7?).

    7. Beam angle

    Beam angle refers to the angle or spread of light from the globe. It is usually only relevant for:

    • lamps with in-built reflectors, or
    • the actual lighting fixture

    If you have really high ceilings there is no point installing lamps or fixtures with a wide beam-angle. You'll just end up having to over-size the light bulb's wattage so that enough light gets down to your work surface or floor. The reverse is also true: if you use lamps with very narrow beam angles, you may end up needing to install many more light fittings than necessary.

    In summary: beam angle needs to be considered in conjunction with the lumen output (see above) so you get the 'lux' levels you are after.

    8. Colour Rendition Index

    Colour Rendition Index (or CRI) is often missing from light-bulb packaging, but can typically be found on the manufacturers data sheet.

    The maximum CRI value is 100, referring to natural daylight and incandescent lighting. The closer a light bulb's CRI rating is to 100, the better its ability to show true colours to the human eye.

    For example, here are some typical CRI values:

    • Candle at 1700k = 100 CRI
    • High Pressure Sodium at 2100k = 25 CRI
    • Incandescent at 2700k = 100 CRI
    • Tungsten Halogen at 3200k = 95 CRI

    What about cost?

    Of course, cost is important. But, once you have checked these 8 critical factors, the cost decision becomes far easier.

    So, next time you buy a replacement light bulb, consider this list, rather than leaving cost as your only comparator.

    Click here to see our complete range of Philips LED Lighting

    - Ryan McCarthy

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