GCSE Physics

New Technology: LED Bulb Tests

How Science Works

All mains LED lamps have to overcome various issues to work, not just the ones we tested from Totalight.

  1. The lamps replace mains-voltage halogens (230 V a.c.), yet LEDs require d.c. at much lower voltages. So the lamps need a transformer built in (to step-down the voltage) and a rectifier to produce d.c. from a.c. All in a very compact unit! There is, however, a very slight delay between hitting the switch and light being emitted. Unlike low-energy CFL lamps, however, LEDs are at full brightness immediately.
  2. 4 W LED bulb [click to enlarge]Until physicists work out how to get more of the light to actually escape the LEDs, they will always get quite hot in use. Transformers also get hot and it has to be got rid of - so these LED lamps are longer than the GU10 halogens they replace to make way for a heat sink. This is made of aluminium (see photo) and has lots of fins to allow air flow around it. Consequently these lamps are perfect for ceiling down-lights (where there is normally more than enough space to take them), but not for directional spotlights.
  3. The dimmable version works brilliantly on a standard wall-switch dimmer, but if you use the LED lamp with standard halogens controlled by the same dimmer, the LED lamp gives out a much brighter light much sooner (in the dimming) than the halogens. This is, of course, because the LED version is much more efficient! We actually found this useful though, as above a table the LED could be quite bright whilst the halogens were barely glowing - great if you just want to sit at the table reading.
    Obviously it would be sensible to replace a whole set of halogens with LED lamps, but the initial cost is quite high and we would recommend trying a couple out before committing to a larger purchase. Unlike buying "new halogens", however, there actually is a "payback time" for the purchase of LED lamps.

Now it's time to look at the issue of Payback Time carefully.

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