Went on a trip to Carrefour the other day and walked down the residential illumination aisle. A 500W 118mm halogen tube went for AR$25 (US$1.60) with no visible indication of its brightness, the same price as 300W, 150W, and 100W versions. An OSRAM 13W LED bulb using 13 watts, supposedly equivalent to 100W incandescent, providing 1350 lumens, was priced at AR$289 (US$18), while OSRAM compact fluorescents using 20W, supposedly equivalent to 85W incandescent, cost AR$90 (US$5.60) and provide some illegible number of lumens which I suppose is about 1150. (The iPhone Notes app peremptorily downrezzed my photos and destroyed the information I was trying to acquire.)
If we assume a luminous efficacy of 18 lm/W for the halogen, it should be 9000 lm.
Historically, the most inexpensive way to do lighting has been with straight fluorescent tubes, like the T8 size. I didn’t happen to see these at Carrefour, but DMX SRL in San Nicolás in Buenos Aires is offering 58W GE T8 tubes for AR$59 (US$3.70). These are F58T8 tubes; one such on GE’s site has 4900 mean lumens. Additionally, for these, you need a ballast; Tienda de LED in Chacarita offers a two-tube RTM electronic ballast for 58W T8 tubes for AR$75 (US$4.70), or US$2.35 per tube.
| type | US$ | W | lm | lm / W | lm/US$ |
| halogen | 1.60 | 500 | 9000 | 18 | 5625. |
| LED | 18 | 13 | 1350 | 103.84615 | 75 |
| compact fluorescent | 5.60 | 20 | 1150 | 57.5 | 205.35714 |
| T8 fluorescent | 6.05 | 58 | 4900 | 84.482759 | 809.91736 |
#+TBLFM: $5=$4/$3::$6=$4/$2
The very low cost of the halogen bulbs surprises me, but it seems like it might make feasible a project I’ve been thinking about for some time, which is making a daylight booth in my house for mood control. Direct sunlight is about 100klux, while indirect daylight is in the 15klux range. In a reflective-walled booth, like an indoor-growing apparatus, almost all of the light would be absorbed by my skin unless the booth got very large; my skin absorbs about ⅓ of the light that falls on it, and has a body surface area of about 2m², so effectively I absorb about 0.7m² of light. Illuminating 0.7m² with 15klux requires a bit over 10klm, which means one or two of these 500W bulbs would be totally adequate. I’d need three if I were black.
Now, 1000W of illumination will require a certain amount of cooling and fire-danger attention. You could get the same 18klm out of LEDs with only 173W, but you'd need 14 bulbs like the one I saw, costing US$240 instead of US$3.20.