Equivalent Wattage

by /u/SuperAngryGuy of /r/HandsOnComplexity

It is important to understand that the light bulbs in your home are rated in wattage equivalent to an incandescent bulb and don't actually use 100 watts. For example, a '100 watt' light bulb is around 1600 lumens and a '60 watt' bulb is around 800 lumens.

The following values are equivalent to an incandescent light bulb (spot and flood lights may be a little different if the manufacturer is using equivalent to halogen lighting). The watts equivalent does not ever change although the true wattage does as LEDs become more efficient. This is to help lower the confusion among consumers of what size light bulb they should get. A lot of low end LED sellers will use '600w' or '1000w' as a deceptive marketing practice, and you need to go off by actual wattage. Also, be wary of any 'watts equivalent' to HPS light.

  • 40 watts equivalent = ~450 lumens
  • 60 watts equivalent = ~800 lumens
  • 75 watts equivalent = ~1200 lumens
  • 100 watts equivalent = ~1600 lumens
  • Greater than 100 watts equivalent is not necessarily very well defined

For a Space Bucket we want 3000-5000 lumens for a five gallon bucket for cannabis in flowering. At the time of this writing a 100 watt equivalent bulb draws about 15 actual watts so we would want about 40-45 actual watts of LED light bulbs. This convention of equivalent watts is not going away any time soon and is useful since we can choose light bulbs based on how much light they give off rather by how many watts they actually use.

Marketing gimmicks

A cheap '600w' LED grow light you might find on Amazon or eBay is not drawing anything close to 600 watts, nor is it 600 watt equivalent to anything particularly HPS (high pressure sodium) lighting. It's a deceptive marketing practice and they will not perform as advertised. I've seen 50 true watt lights advertised as '600w'. Same with the '1000w' and other lights.

Also, you can't make a claim like 'a 600w light is really a 100 true watt light' because the real power draw numbers are all over the place since there are no real standards. Their cheap LEDs are also going to be significantly less electrically efficient compared to quality grow lights, and they will put out around 40-50% less light per amount of energy usage on top of cheap LEDs tending to not last as long. Do not buy these types of cheap and deceptive lights!

An economic metric you might use is umol/sec per dollar or PPF/dollar. If that '100 watt equivalent' 18.8 umol/sec light bulb is costs $2.50 then 18.8/2.5= 7.52 umol/sec per dollar is the cost of the light. As a comparison, a 1000 HPS consumes 1000 watts and outputs 1800 uMol/sec of light. That 1000 HPS lighting setup costs $200. 1800/200= 9 umol/sec per dollar. The HPS provides 25% more light per dollar than the LED light bulb.