Light fitting temperature test

Many existing light fittings are designed for incandescent lightbulbs and are now fitted with LED lightbulbs or the older CFL, Compact Fluorescent Lights, or the versatile halogen alternatives. The physics of each light technology makes temperature a critical factor in life expectancy. What is the temperature in your light fitting?

The old incandescent lights are banned in some countries to force you to buy something more expensive, using the justification of less energy consumption. If the new technology does not last, due to heat build up, you waste massive amounts of resources and energy manufacturing replacements.

The old style incandescent lightbulbs had two styles, standard intensity and high intensity. Standard intensity incandescent lightbulbs produced a warm light around 3000K and lasted 2000 hours. High intensity incandescent lightbulbs produced a whiter light around 4000K and lasted 1000 hours. Some cheap brands would break when you first switched them on.

Light fitting: Daydream Lunar Oyster 35cm takes 2 * 60 watt light bulbs. The following image shows the light fitting with the temperature probe wire hanging out the side.

Light bulbs: Philips EcoClassic 70 watt * 2
Room air temperature: 25.0°C
Air temperature near lights: 25.9°C
Temperature inside light fitting after 1 hour: 112°C

Digital thermometer probe

I used the Digitech QM-1602 from Jaycar because anyone in Australia can buy exactly the same model and we can all share our test results. $29.95 at my local shop.

The front of the box says -50°C to 750°C. The box contains a thermocouple, TP-01, for measuring from -50°C to 204°C. There is an optional, purchase separately, TP-02 probe for -50°C to 750°C. You do not need the TP-02 for measuring the temperature in a light fitting unless the light fitting bursts into flames.

The TP-01 has a tiny unprotected element designed for measuring air temperatures and nothing else. The TP-02 has a long stainless steel probe you could use for hot oil in a frying pan. The TP-02 can also be used for measuring the extreme temperatures in car exhaust gasses.

The supplied battery is a heavy duty battery which is acceptable for one set of tests but do not leave it in for more than 6 months because it will leak. I immediately replaced the battery with a Duracell Ultrablock alkaline good for five years without a leak.

The QM-1602 accuracy is +/- 0.75% + 1°C. A reading of 100°C could mean anywhere between 98.25°C and 101.55°C. A couple of degrees will not make a difference to a light, we are looking for differences of ten or more degrees.

Lightbulb or Lamp?

Lamp is an attempt at an internationally agreed name for a lightbulb, commonly called a bulb or a globe. Lamp is a hard sell when you go shopping or camping because it refers to a light fitting, not the lightbulb or other light source, inside. The arbiter of all things for most people is Google. Google an image for lamp, globe, then bulb. Bulb wins.

Brand

For most tests I start with Philips lightbulbs because they are the most reliable. (Philips refer to their lightbulbs as bulbs on the packet.) Some of the other brands have a wider range of sizes or wattages in our local shops. Some of the other brands break in a few weeks or break when you are inserting them in the light fitting. Some of the other brands are just brands and vary a huge amount from batch to batch because they buy from a different manufacturer each time.

Halogen

For halogen tests, I use the Philips EcoClassic lightbulbs. They have two wattages on the packet, the actual and the equivalent based on older style incandescent lightbulbs. They do not state which style of incandescent they compare to, standard or high intensity. The Philips EcoClassic produces a white light equivalent to the old high intensity incandescent lightbulbs and claim to last the 2000 hours of the old standard intensity incandescent lightbulbs.

CFL

The light fitting is too small to fit most CFLs capable of producing an equivalent light. Some modern CFLs are smaller and fit. The CFLs burn out quickly. I will try them again and measure the heat.

A replacement light fitting designed for CFLs uses a circular lamp. To get an equivalent light output, I would have to buy a fitting 50% larger in diameter, suggesting the CFLs have to run at a much lower temperature.

I have two of the circular CFL lights in my kitchen. They are nearly twice as big based on area. The circular lamps radiate more light than the little CFLs with multiple tubes in parallel. The lamps have lasted a ling time, at least ten times the longest lasting CFL in the light fitting tested in this page. The huge ugly light fittings are cool enough for CFLs.

There are no dimmable circular CFLs which means I cannot use them in several rooms.

I have exposed CFLs in another room and they last due to the free flow of air keeping them cool. The CFLs are mounted on the ceiling beams, not up against the ceiling, giving the CFLs extra air flow. Again, ugly but cool and economical. Just avoid bumping them with you head because you will get an eyeful of glass and a lung full of mercury.

CFL's outdoors are less successful. I have two lights outdoors, protected from the rain but not the hot summer air. Neither one is enclosed so there is no heat build up, just normal Sydney outdoor heat. Both lights are on for less than six hours on a typical week, that is 300 hours a year. There were two light failures during last year and one at the start of this year. Lights advertised as lasting 8000 hours are lasting less than 400 hours.

LEDs

LEDs of equivalent light output have huge bases that do not fit inside the light fitting. Friends report seriously frequent failures of LEDs in enclosed light fittings. Some reverted to other types of lights. Some settled for LEDs producing less light.

Conclusion

112°C is too hot and occurs in part because the light fitting should have only 60 watt, not 70 watt lights. The halogens last a long time despite the heat. CFLs of equivalent light output fail quickly in the same fittings. Halogens seem to like the heat and are the best long term option for that type of enclosed light fitting. A conversion to CFLs will require the installation of big ugly replacement fittings.