Hi I got a 11 watt T2 Helix Energy Saver bulb with specs stating equivalent output is 40 watts.

My lamp says CFL Max 9 watts. Can I safely use this bulb in this lamp or is it a def. no no?

3 Answers 3


The power consumption permitted by the fixture is 9 watts; the bulb that you've selected is 11 watts. You've exceeded the permitted wattage, even if it is by a very small margin.

Is it safe? Most of the max wattage specifications by manufacturers are conservative, so you would probably be fine. But why exceed a stated limit? I would suggest considering a smaller wattage bulb for that fixture, or a fixture that supports the bulb wattage that you've selected.

  • And if the CFL ballast not able to take the extra heat and the desk lamp is constructed in such a way that it contains the heat (closed fixture, open bottomed fixture with no ventillation), 11 watt CFL bulbs will experience early failure. Chalk that one up to experience. Higher quality bulbs may have ballasts built with components that will take the higher heat rating. Otherwise get used to the stink of electronic death every so often. Newer Phillips LED equivalents are getting really cheap, so more light, less heat might be your option. Commented Oct 14, 2014 at 15:28

Read the rating carefully. If it says Max 40 w Incandescent, (CFL 9 W) then you are ok with the 11 watt bulb.

This issue comes up from time to time, and it's due to a misguided belief that a 9W CFL is in all ways equivalent to a 40 incandescent. This is not true.

Very simply, A 40 W element will consume and output 40 W of energy. Incandescents are extremely inefficient in light output, and most of this energy comes out in the form of heat. The fire hazard comes from this waste heat. More explicitly, the danger is in setting the shade of fire. A 40 W bulb emits about 2% of the energy as light, and 98% as heat. This number is so small, we could easily say that the bulb emits it's entire output as heat.

So you lamp is built to be able to withstand 40 w of heat output.

Now, what happens if we stick in an 11 w CFL? Well, The first law of Thermodynamics tells use that Energy in == Energy out. (Incorrectly) Assuming that all of the energy in comes out in the form of heat, this CFL can output a MAXIMUM of 11w of heat. This is well below the 40 w that the lamp was built to withstand.

So, all things being equal, you could put in a 40 watt CFL, which would be equivalent to 180w incandescent. However, the size of the bulb might move it considerably closer to the shade, and introduce fire hazards due to proximity. So Not Recommended


If the lamp is rated for a maximum CFL bulb of 9 watts, then you shouldn't put an 11 watt bulb in it.

If you do, you will be overloading the rating of the lamp by 22%.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.