Incandescent light bulbs produce light omni-directionally so that the light falls evenly through a spherical pattern. LED’s, however, are inherently directional: They perform like tiny spotlights. Designing an LED bulb that mimics the hemispherical light pattern of an incandescent is one of the biggest challenges for bulb designers.
Here’s a simple but practical way to compare the light output patterns of several LED 60W-replacement bulbs, an incandescent bulb, and a CFL bulb. Rather than just take photos of bulbs against a white background, this test set-up uses a white paper ring that angles out around the light source at 45 degrees, bouncing the bulbs light toward the camera which is set at a 1/60 shutter speed and an F21 stop. (Many thanks to my husband Doug Conner and his Canon Rebel.)
Here’s the test set-up:
…and here’s the same view with the room light off and the light-under-test turned on:
This is a head-on photo of how the light looks from an incandescent bulb, which I’ll use as the baseline standard.
The light is evenly bright around the ring, with just a small shadow underneath.
The CFL is similar, with just a slightly larger shadow.
Impressively, the Philips L-Prize LED bulb has an even smaller shadowed area than the incandescent:
You may recall that the L-Prize bulb uses a remote phosphor (that’s what makes the bulb cover that unusual yellow color) and effectively disperses its LEDs’ light in a near-perfect hemisphere. It also makes for a more expensive design: The bulb costs $25. It’s likely that changing to the cheaper sno-cone design, as well as eliminating the dimming circuit, were at least part of the reason Philips is able to sell its new 60W-equivalent non-dimmable bulb for $15.
Both Philips bulbs are 60W-equivalents: If you don’t care about dimming, will the cheaper bulb work suffice?
It depends on how you’ll use it. As you can see, the light is mostly projected out into the top half in a semi-hemispherical pattern. If you expect an omni-directional, even light, the $15 bulb may not suit your needs.
Cree’s new 60W replacement bulb does an admirable job of filling out the hemisphere, with the shadow at the base smaller than the CFL and the same or less than the incandescent. The Cree mounts its LEDs internally on a pedestal with the bulb, and the bulb seems to have a very faint reduction in brightness at the top of the ring. You’d have to have an integrating sphere to measure this, and I believe the difference in brightness is minimal. The Cree bulb, which is dimmable, sells for $13.
(Here’s a detailed tear down of the Cree bulb.)